Nervous about the way LO sleeps?

Well LO is 6 months on saturday and when hes awake he rolls over from belly to back because he hates being on his belly but he wont roll the other way... but when hes asleep! he rolls over on to his belly instantly, and when we try to roll him back, within minutes he rolls back to his belly! This scares me because of SIDS , I really don't know what I should do. Should I let him sleeps as he wants? and how do I stop waking up 30 times a night to check on him because he sleeps like this now? thanks