Oh, god, I started playing it at midnight last night--BAD! IDEA!
Extremely immersive game, and I feel tense even when I go back to a room the game didn't tell me to. For example, I felt extremely tense when I got too anxious to continue playing and I had to make my way back to the save room. The atmosphere is such that I feel like an enemy could just pop out of a vent that I already passed!
I can't wait to get back to it!