cramps night before BFP

The night before I got my BFP I had severe cramps to the point where I was curled up on the floor and of all, I didn't know I was pregnant at that time so I put a heating pad on and lay down when I called the OB after I found out I told him that I had cramps and they said that was normal I didn't tell them how severe the one day was and they haven't been severe since. Has anyone had this happen?