I've been thinking a lot about this and I came to the conclusion it's true. Not only that, but it never gets talked about, nobody mentions it. Probably everybody thinks it's not important.
But really - you spend in bed say ~8 hours EVERY day (night), and you think that doesn't affect you?
Where I'm coming with this is something I realized soon enough: I always sleep on my back. Always always. Rarely, if ever, I get on my belly. Now the question was "why?". And you'll probably say "who cares?".
Well, staying on my belly I always feel like I suffocate, like I'm "trapped", my face is being pressed on the bed sheet and I need to twist my head around to breathe properly, my back feels weird, and all kinds of distressing stuff happens. So I stay on my belly 5 minutes at the most and then need to turn on my back to actually sleep.
So why is all this important and how is this related in actually helping you?
Well let's think about it - why would that happen? And I've came to the conclusion that all this stuff is actually a lack of flexibility in certain areas. In my case, I'm in anterior tilt and the hip flexors are very tight. They pull to "shorten" the angle between the legs and the upperbody, thus pressing my face onto the bed sheet.
Also, the shoulders are not flexible and they make me feel all kinds of pressure on my upperback/neck/head while on my belly.
If you'll actually pay attention to the way you sleep you could find potential valuable info about your flexibility (or lackthereof) for YOU.
A guy who likes to sleep on his belly a lot will probably have very flexible hip flexors yet tight hamstrings, while a guy who prefers to sleep on his back will be the opposite: tight hip flexors and flexible hams (not a rule, but you get the idea).
Now obviously there are tons of positions you can sleep into, but just think about this stuff if you care to.
