Before being diagnosed with Type II Diabetes, every afternoon I would have to lay down and take a nap because I would get so sleepy. I didn't understand why. After I was diagnosed, my doctor asked me if I was unusually tired. She said that after eating lunch, my
blood sugar was so high, it was causing me to get sleepy. As Paul said, he would fall asleep as a result of the huge spike. So it sounds like your spike is pretty big and it's causing you to get sleepy. That could be all it is but it wouldn't be a bad idea to go to you doctor and get a blood lab done just to be on the safe side.