Suddenly big lower FPS

[Romulator]

Since you are recording the game, have you perhaps changed some settings in the recording software which may impede on the game's performance?

If you go to another level in Amnesia, one which did not have the FPS drop, is there still a significantly large FPS drop?

I've known that a few areas around the level you're in are extensively large, as well as some being quite demanding of performance due to processing of many lights, particle systems and fog areas.

I can't help much beyond there, unfortunately. :c