Post-hypnotic amnesia occurs when a hypnosis subject is unable to recall earlier events as a result of hypnosis. Usually these events are restricted to those that occurred within the hypnosis session itself. The memories themselves are still intact.
Post-hypnotic amnesia can be induced intentionally by the hypnotist making a suggestion during the hypnosis session. It can also be induced by the hypnotist utilizing the Zeigarnik effect to close off the subject’s memory of events inside the hypnosis session.
The main reason for inducing post-hypnotic amnesia is to prevent the hypnosis subject from undoing the changes created during the hypnosis session before they can set into long-term memory.
Post-hypnotic amnesia can be permanent, although it is far more common for it to be temporary.