Body temperature has nothing to do with it.
There is a bit of a lag in the process, however, so the level of insulin may not start to peak for about 30 minutes after you begin your meal. Later, the insulin production may not shut off precisely when you need it to. As a result, an hour or so after the meal, your blood sugar may drop below normal, leading to exhaustion and sleepiness. This is such a common phenomenon in colleges and universities that many professors abhor having to lecture immediately following lunch. Try eating a lighter lunch that contains fewer carbohydrates, or eat a piece of fruit when you begin to feel sleepy.