Hypoglycemia, also referred to as an insulin reaction,  is what every diabetic fears -- very low blood glucose. Since the brain requires glucose for fuel at every second,  it's possible to induce coma, seizures, brain damage  and death by letting blood glucose drop too low. Because the brain is almost totally dependent on glucose to make use of oxygen,  it is somewhat like having severe breathing problems. Though the causes and mechanisms are different, in both cases the brain does not have enough oxygen, and similar symptoms and problems can occur. It is caused by giving too much insulin for the body's current needs.
The blood glucose level at which an animal (or person) is dangerously hypoglycemic is fuzzy, and depends on several factors.  The line is different for diabetics and non-diabetics, and differs between individuals and depending on exogenous insulin and what the individual is accustomed to.
The most likely time for an acute hypoglycemia episode is when the insulin is working hardest, or at its peak; this is when blood glucose levels are at their lowest, or nadir, due to the action of the insulin. Mild lows may cause lethargy and sleepiness. 
An acute hypoglycemic episode can happen even if you are careful, since pets' insulin requirements sometimes change without warning. Pets and people can have hypoglycemic episodes because of increases to physical activity.  What makes those with diabetes prone to hypoglycemia is that muscles require glucose for proper function. The more active muscles become, the more their need for glucose increases.  Conversely, there can also be hyperglycemic reactions from this; it depends on the individual/caregiver knowing him/herself and the pet's reactions.
Unexpected or infrequent exercise can mean a "surprise" hypoglycemia episode. Any event that means more than the usual (and planned for) activity, can cause a low, since the food that supplies energy is used faster than expected.  Some extra food before or directly after the exercise or excitement can make this easily managed. Excitement generally means more activity than normal, so it needs to fall into the category of "exercise" and possibly "fed" to avoid low blood glucose problems. 
According to a 2000 JAVMA study, dogs receiving insulin injections only once daily at high doses  are more likely to have hypoglycemic episodes than those who receive insulin twice daily.
Symptoms and TreatmentEdit
The symptoms are:
As soon as possible, administer honey or corn syrup by rubbing it on the gums (even if unconscious, but not if in seizures), and rush it to the vet. Carry more honey or corn syrup with you on the way and keep rubbing it on the gums, where it can be absorbed -- it could save the pet's life. Every minute without blood sugar causes brain damage. Some recommend administering syrup anally, with a feeding syringe or dropper, if the animal is in seizures!
NEVER try to make an seizing or unconsicous animal swallow. The food or liquid could possibly choke him/her. There is also a chance that the materials could be aspirated (wind up in the lungs instead of being swallowed). 
Intervet suggests an especially good place to also rub sugar, syrup or honey is under the pet's tongue.  Reading the Wikipedia definition for the medical term of administering a drug or substance under the tongue, sublingual.  makes it clear that the high concentration of blood vessels present means rapid absorption and passage to the carotid artery, which is directly connected to the brain. In hypoglycemia, this would provide the brain with the glucose fuel it needs to make proper use of oxygen.
A photo link below  of how to apply corn syrup to gums.
Symptoms of hypoglycemia should always be taken seriously and addressed promptly. Better to risk treating a "non-legal" hypo than to fail to respond quickly to the signs of actual hypoglycemia. 
"Hypoglycemia is deadly; hyperglycemia is not. Owners must clearly understand that too much insulin can kill, and that they should call a veterinarian or halve the dose if they have any concerns about a pet's well-being or appetite. Tell owners to offer food immediately if the pet is weak or is behaving strangely."
Serious hypoglycemic episodes need medical attention. At a hospital or Emergency facility, infusions of dextrose can be administered, and if need be, the hormone glucagon can also be used, as in the treatment of people with diabetes when there is a serious low blood glucose problem. 
Its also important to remember that it takes a little time to fully come back from a hypo incident. In people, cognitive function is impaired at levels below 54mg/dL. Full recovery from the hypo can take 40-90 minutes after blood glucose levels have returned to normal.  Like insulin, the sugar given doesn't have a total effect instantaneously.
Sometimes a mild hypoglycemic episode will go unnoticed, or leave evidence such as an "accident". In these cases the blood sugar will often be paradoxically high upon the next test hours later, since the pet's body will react to the low blood sugar by stimulating the liver to release stored glycogen. This condition is known as Somogyi rebound,  and requires a lowered insulin dosage for the next few days. The Somogyi rebound may also occur when the pet's blood glucose drops too rapidly, even if it never actually reaches a low reading.
A single hypoglycemia or near hypoglycemia episode  can result in hyperglycemia for up to 3 days following it. In response to the threat of low blood sugar, the body releases counter-regulatory hormones intended to raise bg's; the body's way of trying to save itself.
Ahh, thanks for that. I'm not kwnlledgeaboe enough to be able to referee this point, but I can now see your case. Gluconeogenesis can be a real bugger for me sometimes. It really kicks into action for me in certain social situations, thereby turning on the Fight or Fight hormones like cortisol, which in turn counteract the insulin in my system and completely throw me out of balance. What made you choose biochem' over molecular biology (I say this realising that they overlap a lot)? Ahh, thanks for that. I'm not kwnlledgeaboe enough to be able to referee this point, but I can now see your case. Gluconeogenesis can be a real bugger for me sometimes. It really kicks into action for me in certain social situations, thereby turning on the Fight or Fight hormones like cortisol, which in turn counteract the insulin in my system and completely throw me out of balance. What made you choose biochem' over molecular biology (I say this realising that they overlap a lot)?
Fast Drops in Blood GlucoseEdit
People and pets can also exhibit signs of hypoglycemia if their glucose levels drop rapidly.  This is true with the use of all insulins, even though glucose values are not in hypoglycemic range. 
For example, let's say someone's bg is at 400. He/she uses fast or rapid-acting insulin for corrective purposes which lowers the blood glucose values to 200 within an hour. The meter says 200, but there are signs of hypo. The body responds to the rapid drop as it automatically is meant to, sending out hypoglycemic warning signs, even though the 200 reading is far from hypo levels.
The system can only determine that blood glucose levels are falling at a rapid rate, not whether they are "supposed to" in this hypothetical case, and sends out "hypo" warning signals to protect itself.  This may include glycogenolysis, leading to a Somogyi rebound, or it may not.
Warning signals in dogsEdit
Inflamation of the eye blood vessels in dogs is an indication of hypoglycemia. In both hypoglycemia and hyperglycemia, the whites of the eye become reddened and appear quite irritated. The difference is best likened to the difference in the color of venous blood and arterial blood. Venous blood is of a darker red than is arterial blood. In hypoglycemia, the inflamation is of a "venous blood" color.
In both hypoglycemia and hyperglycemia, the inflamation lessens as the proper bg corrections are made, reverting to no visible irritation when euglycemia is achieved. The symptoms were first discovered with an individual dog, and extended to all diabetic dogs in the veterinary practice. All presented with the same degree of eye inflamation for hypoglycemia, hyperglycemia or lack of it for euglycemia. The eyes were examined prior to blood testing, which confirmed the eye results each time.
Tight control and hypoglycemia unawarenessEdit
The question of why some diabetics exhibit more overt signs of low blood glucose than others came up in a talk with a Certified Diabetes Educator who is also a registered nurse. Her response was that the better one's control is, the lower someone's blood glucose can go without them feeling or showing signs of illness. It has to do with the blood glucose levels not dropping as far and thus the body doesn't feel the need to send out as many "warning" signals.
Therefore, if one is always primarily high, he/she would show more physical responses to low blood sugar levels than someone whose control is tight. (Going down 25 floors rapidly in an elevator may not make your ears "pop"--going down 50 rapidly likely will.) Personal experience says this also holds true for canines with diabetes; those in tight control can show few, if any, hypo symptoms even though the meter says otherwise.
Dr. Orzick, a professor at Baylor College of Medicine in Houston, also says that the rate at which blood glucose levels fall is the primary reason for lack of body warning responses.  He also offers an opinion regarding longer-duration insulins: that for some using them, blood glucose levels fall at rates too slow for the body to recognize and thus set the hypoglycemic warning responses into action.
Many humans with diabetes suffer from what's known as hypoglycemia unawareness. This means they often have no physical warning signs they are low and approaching hypo status. There's been much research regarding the unawareness factor in the human diabetes community but for the most part, there have been few real solutions. Those with this condition must test many, many times a day, as they have no other way of telling whether they are too low or not.
What has definitely been learned from all the human research into the problem is that having serious hypoglycemia episodes puts one at risk for becoming hypoglycemia unaware. A person who is a "long time" diabetic can also become unaware, due to the subtle changes the disease makes in the body over time.
Those who have suffered bouts of serious hypoglycemia are also more at risk, unfortunately, to have more of them, as opposed to persons with diabetes who have never experienced any serious hypoglycemia incidents.
Medication warnings mentions medications that can cause problems with hypoglycemia.
- ↑ Hypoglycemia. American Diabetes Association.
- ↑ Glucose and Brain Metabolism. Diabetes.org.
- ↑ Irvine, Andrew J., Butterwick, Richard, Watson, Timothy, Millward, D. Joe, Morgan, Linda M. (2002). Determination of Insulin Sensitivity in the Dog: An Assessment of Three Methods. American Society for Nutritional Sciences.
- ↑ 4.0 4.1 Glucagon Infusions. Southpaws.com (Fall 2000).
- ↑ Auer, RN (2004). Hypoglycemic Brain Damage. Metabolic Brain Disease.
- ↑ Hypoglycemic Effects. InChem.
- ↑ Jess, a vet tech with diabetes experience, describes different levels of "hypo". Feline Diabetes.com.
- ↑ 8.0 8.1 8.2 8.3 Diabetes Mellitus-Hypoglycemia. Animal Hospital of Pierce County.
- ↑ 9.0 9.1 9.2 9.3 9.4 Hypoglycemia. Intervet.
- ↑ 10.0 10.1 Cook, Audrey (1 April 2010). Identifying the reasons behind difficult-to-control diabetes in dogs. DVM 360.
- ↑ 11.0 11.1 Diabetes Mellitus. Gulf Coast Veterinary Specialists.
- ↑ Variables affecting chemistry results. Cornell University.
- ↑ Cat-Dog-Diabetes-Hypoglycaemia. Intervet UK.
- ↑ Hess, Rebecka, Ward, Cynthia (2000). Effect of Insulin Dosage on Glycemic Response in Dogs With Diabetes Mellitus. JAVMA.
- ↑ Fleeman, Linda, Rand, Jacqueline (2000). Long-Term Management of the Diabetic Dog. University of Queensland.
- ↑ Seizures. Washington State University.
- ↑ Hoenig, Margarethe (March 2003). Diabetes in Pets-Monitoring-Page 2. Diabetes Voice.
- ↑ Thomas, WB D.V.M Dipl.ACVIM (Neurology). Hypoglycemia. Canine Epilepsy.com.
- ↑ 19.0 19.1 Vetsulin-Diabetic Dog Owners--What To do-Low Blood Sugar. Intervet.
- ↑ Caninsulin Guide-Page 9. Intervet.
- ↑ Sublingual. Wikipedia.
- ↑ Photo-Applying Corn Syrup to Gums for Hypoglycemia. Pet Education.
- ↑ Hypoglycemia-Page 7. Novo Nordisk.
- ↑ Cook, Audrey (2007). Latest Management Recommendations for Cats and Dogs with Nonketotic Diabetes Mellitus. DVM 360.
- ↑ Cook, Audrey (2007). What Clients Need to Know. DVM 360.
- ↑ 26.0 26.1 26.2 Hypoglycemia-Dogs. BD Diabetes.
- ↑ Ask the D Team. Childrenwithdiabetes.com (2005).
- ↑ 28.0 28.1 Hypoglycemia-Page 4. Intervet.
- ↑ Hypoglycemia. Yorkshire Diabetes.
- ↑ Pounds to Kilograms/Kilograms to Pounds online converter. Open Toronto.
- ↑ Insulin Administration Guide-Insulin Shock/Hypoglycemia. Veterinary Partner.
- ↑ Greco, Deborah. Ask Dr. Greco: Canine Diabetes. BD Diabetes.
- ↑ Hypoglycemia-EASD. Close Concerns.
- ↑ Hypoglycemia-Rebound. Diabetes Self Management.
- ↑ Vetsulin-Treatment of Diabetes Mellitus in Dogs-Page 21. Intervet.
- ↑ Church, David B. (2009). Logical Approach to Weakness and Seizures. WSAVA.
- ↑ Novolog-Precautions-General-Page 7. Novo Nordisk.
- ↑ Humalog-Precautions-General-Page 6. Eli Lilly.
- ↑ Nelson, Richard. Complications of Insulin Therapy in Diabetic Cats-Page 4. Waltham USA.
- ↑ Hypoglycemia Unawareness. Diabetes Self-Management.
- Hypoglycemia in Dogs Petplace.com
- Treating Hypoglycemia (UK site)-Sugarpet.net
- Hypoglycemia Symptoms,Causes and Cases
- Management of Insulin Overdose-Pages 1-6 Schermerhorn, Thomas, 2001, Standards of Care-Compendium
- Glucagon Infusions Southpaws, Fall 2000
- The Hypoglycemic Crisis Southpaws
- Diabetic crises: Recognition and management (Proceedings) McIntyre, Douglass, April 2008, DVM 360
- Hypoglycemia and some possible causes of it Cornell University
- Endocrine Emergencies Wallace, Melissa S., 2001, Atlantic Coast Veterinary Conference
- Hormones Which Raise or Lower Blood Glucose Clinical Chemistry
- Dog ear infection Southpaws, Fall 2000
- Pancreatitis in dogs Southpaws
- Ivermectin for dogs Schermerhorn
- Cornell University-Feline Health Center-Recognizing & Treating Hypoglycemia Flash Movie
The movie is geared toward diabetes in cats; the concepts of hypoglycemia and the need for prompt treatment make it valuable for all with diabetes.