Same here..
As long as I am tired, I can go down. And I also have this talent for being able to fall asleep within minutes of closing my eyes literally. I never end up laying there trying to fall asleep like other people, I just close my eyes and go.
I am about to go do that right now!!
I am the same way, Only I don't even have to be tired. Just put me somewhere where there's nothing going on (or at least nothing that interests me) and I feel I have no options (have to listen to someone boring talk) and I can go out in minutes.
No stimulation = ceo sleeping.