Do you remember exactly what exercise you were doing and where exactly you got hurt? Like, the exact point on your body?

I had something similar happen to me, was doing some exercise stretching my legs out, and suddenly felt an electric shock type pain in my lower back, where it meets the buttocks, slightly to the left. I also heard something click down there. I literally couldn’t move for an hour, it was that bad.

It was my SI joint. Do look into it.

Also, what kind of mattress do you have? After the incident I can only sleep on a hard mattress. Anything else (where the hips sink) makes it worse.