D'erlanger ~Yuuwaku no Inma Byoutou~

You play as a patient who awakes every night to find the hospital becoming a hellish place--only wake up the next morning and seeing that everything seems normal again. You find out that the bizarre world you visit is called “Mirage”, and that both you and a fellow patient travel there every night. There are those amongst the hospital staff who are trying to tap into this realm; it’s up to you to find out exactly who, and what you’re going to do about it.

[by White Masq]