Insulin coma. A little piece of history here. Many years ago (pre-ect) Insulin coma ("ict") was a form of treatment for people who were psychotically depressed, schizophrenic, etc. This was done on special units in psychiatric hospitals, and level and length of coma were strictly regulated so that people did not die. Much safer, more effective treatments exist today. http://tinyurl.com/n6cloku.
Insulin shock kills. Insulin shock can and does kill, both in homicides, suicides, and accidental suicides. As of lately it has been found that the cause of death in many diabetic patients was the result of over zealous attempts by the medical community to get their diabetic patients under tight control. This led to fewer complications but also more deaths in the patients in the tightly controlled group due to Insulin induced hypoglycemia in the the middle of the night.
In theory. But i've never seen it in real life. It's mostly featured in tv shows and murder mysteries.