Hypnosis is an altered state of consciousness characterized by a state of awareness combined with a heightened state of suggestibility. It is often used as part of a routine of psychotherapy.
In House's Head, Chase uses hypnosis in an attempt to get House to remember the events leading up to the bus crash.
In Dead & Buried, Chase uses hypnosis on Iris to deal with her dissociative identity disorder.
Hypnotherapy at Wikipedia