Fell flat on my back

Nadine
I'm 29w 1day... today I fell flat on my back. I was fine right after. My back is not hurt but now a few hours later I'm having cramps. I'm worried something might have happened to my baby :/ I was sure nothing happened, I felt fine and he's well protected in there but I read horror stories about the possibility of the placenta detaching. Should I get it checked?