Orgasm??

So random! Last night while I was asleep I felt something I'd liken to an orgasm.. But it radiated period pain through my lower tummy, I also might have been "holding on" too long while I was asleep.. When I went to the loo it took me ages to empty my bladder. The period pain left after about 5-10. No spotting or cramping just this random event. We've already seen baby's heart beat so I feel confident baby is ok but has anyone experienced anything like this before??