I might get some Flak for this, but there was this one special encounter I will forever remember because I was so freaked out, I was shaking for a good 10 mins afterwards. This was about half a year ago. The game? You just lost Doom 3.
Yes, I know, I know, the very pinnacle of jump out scare games practically had me shitting my pants. Don't judge me. Anyway, I often play through single player games quite a few times over, and I was amazed at just how much little extra stuff that they managed to jam into that game that I had still missed even after a good half dozen playthroughs. One will haunt me for the rest of my life.
Scenario: Delta labs, the one area with the Conveyor belt with the Imp's in test tubes that give off light. You know the one. Anyway, after the tube turned a corner (and I put a rocket into an imp's face) I noticed a plasma gun lying on a box. I facepalm myself for not seeing this obvious trap, but I went and grabbed it. The result? The most terrifying 15 seconds of my life. Floor dropped, screen turned red, dramatic music, 3 imp's start tearing me a new one, I shoot a rocket point blank (Killing the imps and leaving me with around 15 hp), and quickly get the fuck out of the hole.....only to find that the tube is long gone leaving eveything pitch black, and the sound of 6 more imps all cry out for my soul from all around me.
I survived the encounter (Barely) but the worst part of the game (In my opinion, the conveyor belt is the most unnerving part for me) just got a metric shit ton worse.