Contractions only after peeing?

So last night, I got up to pee and when I got back to bed and laid down, I'm pretty sure I had a contraction. It felt like a really bad period cramp and lasted about 30 seconds and went away. I laid there trying to see if I would have any more, but I didn't feel any and fell back asleep. Well, I woke up and had to pee again, and it happened again! But this time it lasted about 40 to 45 seconds and non after that. Anyone else have this happen?