I can only reply as a diabetic. But if I inject myself with insulin, and I don't either have a high blood sugar and/or eat carbs to cover the insulin, the insulin will shuttle a proportionate amount of sugar out of my blood into fat cells, and leave me without enough sugar in my blood to feed my brain. I will have a hypoglycemic episode. Depending on the severity, I may just need to eat a little sugar. I may need assistance from my husband, or the EMTs. I may have to go to the hospital for a glucose drip if its bad enough. I can go into a coma, possibly forever (my mom was in one for 3 days, and delusional for 4 more after she woke up because of low blood sugar). And if its really horrible, and I get no help, I can die.
29 years old, type 1 diabetic with insulin resistance -- HORRIBLE a1c, and borderline cholesterol problems. Carb addict.