Believe it or not, I've heard of this before. It's some sort of security mechanism that some adults can't ween themselves off of.

I don't see it as a big deal though as most prefer it to sleep. I cross my arms to sleep no matter what position. Back, stomach, side, I cross my arms because I really don't know what to do with them. I guess some people suck their thumbs. It's not a big deal unless you suck the thumb while I'm talking to you about something important (or something benign, or in front of anyone but your spouse)

What ever makes you comfortable I guess.

A year or so back MTV had a show called "Making the Band" It was a reality show where these kids who won some sort of American Idol type contest moved to New York and had to create an album with Diddy (the artist formerly known as P Diddy). One of the kids on the show, Chopper, was supposed to be some kind of hard core gangsta type... but he was always sucking his thumb. I'm not just talking a little thumb sucking here and there. He was sucking his thumb on 80% of the tape they shot.

Gangstas suck they thumbz.