What Causes An Indentation In The Back Of The Head?

a few days ago we found a dent/crater in the back of my husbands head, about 2 inches up from the neck, it was never there before. he has a migran problem but the past few days they have been server. he is having impaired vision, feeling a little bit neusious, and his anxiety has been extremely high the past few days as well (he has anxiety and deals with it very well) he also has diziness sinus pain and some tingeling when he clentches he jaw he gets tingeling around the dent in his head. we dont know what to do or what it may be. help please