One of the most incredible feats people under hypnosis are able to perform is the ability to remember details of a past event that a person has consciously forgotten. Hypnosis has even helped people retrace their steps and remember locations of, say, lost items or valuable papers.
Hypnosis does have the power to tap into memory in ways that other techniques do not. Most importantly, it has the ability to induce temporary, reversible amnesia. This condition is extremely rare, as many amnesiacs don't recover their memories, and some unlucky ones can't make new memories.
Although not all hypnotized patients can have their memories suppressed, and no one suppresses their memories unless they're told to, the effects can be startling. For one thing, the entire memory can be brought back with a word. This indicates that hypnosis doesn't obliterate memories, it just temporarily shuts off the retrieval system. One woman was told she couldn't remember the word 'six,' and so answered 'seven' to mathematical questions. A man forgot his own name. Any memory could be suppressed.
But the memory didn't go away. A group of students were hypnotized and told to forget a short film they had just watched. While unable to answer questions about the film, they had no problem remembering if the film was, for example, shot on a handheld camera. It was only the content that was suppressed. This ability to remember and react to the context of a thing without remembering the thing itself is the post-hypnotic suggestion. It's a suggested habit that makes sense in context (like reaching for a cell phone when hearing a ringtone) but not at that moment (if you deliberately left your cell phone at home). It just doesn't occur to the person to think of what they're reacting to before they react. Another amazing hypnotic ability is suppression of pain. While it makes sense that people might feel less self-conscious, what with the part of their brain that feels self-consciousness offline, and that their perception might be altered by the part of the brain that governs perception, but pain is different. One of the primary functions of pain is to force someone out of the reverie they're in and make them pay attention to reality. Pain is the outside world breaking in.
But scientists studying perception think our experience is shaped far more by what we expect the stimulus to be than the stimulus itself. There are ten times as many nerve fibers carrying information down as carrying it up. Most people will have experienced feeling a shape in their pockets and being disoriented until they remember that it's a wadded up receipt, at which point the sensations seem familiar.
More to the point, most people will remember an itching or sting that, when they see a more serious injury than they expected, will blossom into pain. A hypnotized person undergoing surgery, for example, may be able to convince themselves that they're experiencing the discomfort of a bug bite instead of a scalpel. That, along with a state of enforced relaxation, can make all the difference.