Even tho I play horror games with headphones and with the lights out, like they suggest, my reactions are mostly in game reactions, like looking around like crazy, reacting to every sound, taking a bit of time to walk forward, running the hell out of the place I'm in, and a bit of swearing to complete it.
I didn't yet play Amnesia a lot, so my best moment would be from the final part of Penumbra Overture, where there's a corridor and human silhouette in the other end of it, waiting, and I stood there looking at it for like 3 or 4 minutes, scratchin my head and wandering if I should walk forward. lol