It's been a very long time for me. About when I played the original Aliens vs Predator. I still have nightmares with things hurdling down long dark hall ways on the walls and ceiling at me. Ok, I exaggerate, but seriously my shoulders and neck ached! I also remember being tense playing System Shock 2. I figure after you've done a couple of scary ones, you get acclimated and then you are immune.