Shortly after the ghost cuts the girl's throat, Dr. Stringer is holding Kristen while the nurse is giving her a shot. When it cuts to a close up of the shot, Dr. Stringer is gone, then reappears after the camera cuts back.
Kirsten is shown picking a lock with a letter opener, that is not really possible, you need a two piece set to open a lock, especially a secure one such as they would have in a lunatic asylum.
Although Electroconvulsive therapy (ECT), formerly known as electroshock, is still used today in the U.S., it is only used as a last resort, with patient consent (except in the most extreme cases), and with the patient anesthetized, not awake and screaming like a tortured banshee as depicted in the film. Also, the ECT machines used in the U.S. today make the procedure quick and relatively painless (e.g., no noticeable twitching or spasming of the muscles). However, the movie is not set in present time but rather in the 60s, as Dr Stringer revealed during his last session with Iris.
It makes no sense why they would place Kristen in the car, and then handcuff her.
The story takes place in 1966, but the ambulance is a 1968 Cadillac.
The word "aggressor" is misspelled as "agressor" in Dr. Stringer's notebook.