I have noticed that exposure to sunlight makes me tired. I recall a friend mentioning something about a specific vitamin or something that was created when in the sunlight that caused the effect and I'd like to find out what it is, and if there is a way I can prevent it.
You have trained your body to the point when you get warmer than room temperature your brain thinks, "sleepy time."
So you have trained your body every night hoping into bed with warm blankets. Body tempature rises and you fall asleep.
Step out into the sun, body tempature rises, brain thinks oh must be time to sleep.