I had a friend years ago that was a type 1 diabetic. I was one of his work emergency backups in case he went into insulin shock or became incoherent. Many times he would get lethargic, have trouble keeping his eyes open, and would start to slur his speech before injecting himself with insulin and coming right out of it. Made me nervous watching this, because you could see the difference. In short they have to be very very careful to regulate correctly. Not eating enough, eating the wrong things, not eating at the right time, exercising too much and not changing the dosage of insulin that day to compensate, etc. Very tricky.