Disclosure before starting it. When you get to the library create a save on the first floor of it and don't save until you make it to the auditorium. The reason being is if you reload the game on a save upstairs from the library the game will glitch up and not allow you to continue. This happened to me twice and with trial and error I found out that was the problem. You've been warned
I'm just going to give useful tips for nightmare
-hide in objects that allow you to hide and make sure it brings your characters mental state to calm.
-mark on your map where a hiding spot is at when you are there so you have a quick place to run back to.
-use caffeine pills when you are dying and are already at horrid mental state. Heals you and doesn't affect your mental state giving you some valuable time to find a hiding spot.
-use coffee and tea in emergencies. Supplies are limited. If you can use a cola to get you to a hiding spot or out of a tight situation use it.
-I recommend just trying to beat the game with any ending to avoid frustration.
-save often but not in the area mentioned above. Also, keep multiple save slots.
-spam the map. It gives you time to plan your next move
I hope these tips help you out, and it shouldn't be too hard. The game is about 2-4 hours long