One of the things about Amnesia is that its damn scary. So scary in fact that you sit in a state of tension for about as long as you play - especially if you play it alone and at night like I do. The trouble with it is that I can only play it for short doses, about an hour, which is fine for a videogame as it makes it feel much longer than it likely is. The trouble occurs when you're involved in a roleplaying game and the tension starts getting unbearable.
If it were a videogame, you'd switch it off for now, head into the light, and come back later (perhaps tomorrow). If you're sitting around a table, you have to either take it on the chin or break that tension somehow. Perhaps you go to the toilet and take a few extra minutes in the light. Perhaps you head into the kitchen for a Milo. Perhaps you start making random television references and start making ridiculous jokes - out-of-character, of course, because in-character nervous banter often just raises the tension as much as it breaks it.
Which one are you?
Heck, sometimes its the Storyteller who will break tension - which can be quite problematic as they've got a far greater tool kit for damaging immersion. A random joke masquerading as in-game description. A silly NPC popping up for comedic effect. They can certainly find a way to pop that tension balloon.
So what to do?
Well, firstly acknowledge that this is making you tense. Hell, you can reduce tension for yourself without damaging other people's tension by simply stating it aloud: "Gawd, this is intense" or "This is scaring the $#@! out of me." It'll make everyone else MORE tense but you might find some relief in camaraderie or simply by taking the distance and the time to ponder your own feelings.
If that doesn't work, try making those comments and bits of banter in-character. Yes, its not a perfect solution because it generates tension to feel your character's desperation but it should make it more palatable. People make jokes to comfort themselves and to take comfort in other people's receptivity to those jokes. It'll still help you get through this.
If you really need a break RIGHT NOW than quietly excuse yourself to grab a coffee and drink it in the light for a few minutes or take a toilet break where you actually check your Tweets or something. That way you can take a break from the tension without popping it completely.
And be aware that you are one of the lucky few who have been able to experience such tension in a game. Its a great way to get that adrenaline going without ever actually being at risk of injury.