Fall asleep in 3 easy steps.

1. Lie down.
2. Let your body temp drop.
3. Put on a blanket and raise your body temp.

I never noticed a pattern, until one day I was lying down and chatting to my sister on the phone, and I said "I've just gotten cold. Now I'm putting a blanket on, and then I'll probably fall asleep!" and she said "Yes, it's true, that's how I get pre-schoolers to have a nap. Boost the air con, then put the blankets on them." So it's a fact.