Mental Hospital Massacre

by Kyle A
(Pennsylvannia, USA)

What is the name of this 80's or 90's horror movie that takes place in a hospital? It may have been based on a Stephen King novel.

The end of the film takes place in a mental hospital. All of a sudden, there is screaming and violence and blood gets splattered on the small viewing window. The door mysteriously opens and as the man steps out into the hallway he realizes that everyone is dead and blood is engulfed in the hallways.

Does anyone know what this is?