I am 27 and have this problem too for years but it comes and goes and is really annoying and depressing for me. as I've known, this problem is most of the times psychological, as it's been for me, unless you feel that it happened IMMEDIATELY after a hit to your head. so after a hit or crash, if you sneezed and after a few days or weeks it stopped, it's still psychological and if you don't care or think about it, sneeze can return eventually.