||A coma from too much blood sugar (hyperglycemia) usually only occurs in people with Type 2 diabetes (non-insulin-dependant, adult onset diabetes). In healthy people, insulin regulates the uptake of sugar from the blood. |
People with Type 1 diabetes who ingest too much sugar will typically have a range of symptoms before succumbing to "ketoacidosis," a condition where the sugar can not be taken up by tissues and this triggers the body to use alternate fuel sources, such as fats. The breakdown products (called ketones) of these fuel sources saturate the blood, and can cause permanent damage and death. In people with Type 2 diabetes, the lack of usable sugar never triggers the use of alternate fuels. The brain, starved of fuel, shuts down its higher brain functions, and the person slips into a coma. Lack of treatment will result in death.
Again, in healthy humans there are mechanisms to regulate blood sugar and ketones in the blood. This does not mean that too much sugar isn't bad for you. There is only so much sugar that the body's tissues can take up and store over a given amount of time. Pushing this limit risks damage to the kidneys, from both accumulation of the sugar and the extreme dehydration it would induce. It is possible that a significant amount of dehydration could induce lethargy and perhaps passing out. Hyperglycemia in non-diabetic patients is usually only a risk when the patient has a sustained infection or illness or is on medication that can raise their bloodsugar levels. For more information, I suggest WebMD.