My Mentor Called Me to the World of Cthulhu

I traveled through time and became an intern nurse in a lunatic asylum. I was bound to the "Recorder" system and could quantify madness using sanity points. On the first night of employment, the late mentor turned into a monster and handed over a note: Before midnight, go to the archives room on the fourth floor and find the blue folder. The system pops up survival rules - only by following the rules can you survive, but the last one reads: Don't believe in rule three. Under the gray fog, truth and madness are awakening at the same time.