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it is the proper way

When you're really tired or really sleepy, you can sleep in any position. I can sleep while standing up in a moving train. Then again, it is better for us to sleep on our backs or on our sides.

wdym there are people who don't sleep on their back?

I can only sleep that way lol.

Yeah, it's hard to sleep that way.

Though, of course I agree with @magnacarta that if you're tired you can sleep in any position.