I have the same thing. Don't know exactly why though. You should be OK.
I get them more often than just laying down, but I notice this too.. My theory is because the muscles are tense and tight, and then suddenly relaxed by laying down.. try laying down slowly, using your arms, and not your stomach muscles, to see if this makes any difference.. I get the same thing... weird. :P
I'm 22wks 3days. I know that they say they are normal but I only get them when I am laying down. Well, maybe I have them other times and just don't notice. Who knows. I'll be fine with my pregnancy, I'm sure. Mentally, who can tell? (I also have a very "spirited" 3 year old and a hubby with the flu).
How far along are you? I've been getting them for about a week now - I'm 20wks+. It seems to me that I only get them when I'm laying down, too. I think it's because when we're laying down, we're more relaxed. Just as long as they don't become overly painful and regular, you'll be fine. I'll be fine. I hope, lol.