I too have trouble trying to stay awake when I'm hunting from my treestand on all day hunts. Whenever I feel like I may go to sleep I play it safe, and crawl down from the tree to take a middday nap. I usually don't sleep for more than 45 minutes at the most.

I used to always hunt from the ground, and used to sleep quite a bit during the later part of the season. The first buck I ever killed woke me up from a nap when he was crossing the creek. I also killed a doe once after she woke me up from a nap; ironically these two situations both took place in the same area two years apart! Maybe I should sleep more often.