Been free diving for little over a year and never had this happen. Started at about 50 feet and everything started off fine. At about the 5th dive I noticed a sharp pain right behind my ears like in the back of my head. I also felt pain in the top part of my teeth. I waited a couple minutes and couldn't go ten feet under without the same pain coming back. I waited a little and tried again same pain. Then i decided to not invert and slowly descend with flippers toward the bottom. Everything was fine. So I just felt the pain when I was inverted and dove down. I could equalize my ears fine it was just this pain in my head. Anybody heard of this before?