Crawling while sleeping???

I just keep on putting her on her back... but she rolls n then keeps her knees in prayer position n her chest n head resting on her bed... n wen she is changing position she moved in front a little n again same position she falls asleep... how can I stop this? She looks so uncomfortable to me... though she is sleeping better even with so much noise... usually she is a very lite sleeper... pls help mommas... does ur 4.5 months old does this too? I would love to hear tat too :)