feeling scared all of a sudden..

I'm 34 weeks today and I have been having nightmares of my baby being harmed or not alive and it's terrifying me. I'm afraid of everything like. What if the umbilical cord gets wrapped around his neck in the womb. Or my biggest fear SIDS. what exactly causes sids..? They say keep toys and blankets and pillows out of the crib but how could that actually cause death? Newborns can't roll over. So how could the suffocate..? And is it possible they could spit up in they're sleep and choke..? Any suggestions on how to put them to sleep for less chances of SIDS..?!