Ok this may sound like a joke, but it's completely true. I was doing abdominal exercises on the floor two months ago. I was on my side and I did a few sets of this exercise where I liftes my torso up up and lifted my legs at the same time. This put a lot of pressure on my butt, but I ignored it. Immediately after doing the exercise, I had a dent in my butt. I wasn't worried, but it won't go away and I think it might be bigger. It is not visible when I am standing but when I lift my knee up to my chest it is plainly visible and about the size of a golfball. What is wrong with me?