Here’s a thread where I answered another hypnosis question:
http://boards.straightdope.com/sdmb/showthread.php?threadid=40760
First of all, the hypnosis you see on TV or in any other entertainment-type atmosphere is going to be just that-- entertaining. Most hypnosis is less exciting than that, and for the simple reason that the purpose of hypnosis is relaxation. In acts where people do funny things “under hypnosis”, I honestly doubt they truly are hypnotized. Given that they’re on stage, with hundreds of pairs of eyes and lots of cameras on them, I think it’s very likely that they’re just cooperating with the instructions of the “hypnotizer” so as not to look (more) stupid.
I have been hypnotized about four times now, each time lasting a short five to ten minutes. Ideally, they should last at least about twenty minutes, even longer if possible. I, along with my fellow psychology tutors, was hypnotized by a professor. What basically happens is that the hypnotizer talks the person into an extremely relaxed state. How well the person is relaxed in this manner depends on both the willingness of the hypnotizee to be led, and the ability of the hypnotizer to provide the suggestion. How well the person is hypnotized at all, for that matter, depends on the same interaction.
Once relaxed, you may be asked to visualize scenes. You may be asked to “interact” with these scenes. (This is the extent of my experience with hypnosis, and though it sounds limited, it’s really everything. You’ve heard of people asked to pretend they were chickens, or Elvis. It’s the same thing. You’re basically envisioning a scenario and acting appropriately.)
It’s important to note that the relationship between the hypnotizer and the hypnotizee is an active process. The hypnotizer provides the suggestions; the hypnotizee provides the follow-up to these suggestions. Contrary the idea that only one of them has any “power” over the other, what it really is is a partnership.
As a hypnotizee, you are fully aware of what’s going on. You know that you’re hypnotized. You know what you’re being asked to do. Although you may be asked to visualize being somewhere else or someone else, at some basic level you’ll always know who you are, where you are, and what you’re doing.
What goes through your mind when you’re given a suggestion (“Picture your hypnotizer naked!”) depends on the details of the suggestion given. If the hypnotizer says “Imagine me naked. I’ve got a nice, tanned body, and I exercise regularly. You really like how my body looks”, then you’ll probably follow the suggestion, and be turned on by his body. I say “probably” because of a second factor-- what runs through your mind will also depend on how deeply you are hypnotized. If you had reservations about the hypnosis, or resisted being totally relaxed, then you won’t totally follow the suggestion. You might think to yourself “But I really prefer pale, flabby bodies!” If you’re that detached from the procedure, then you chances are you will begin to pretend you’re into it.
It’s important to distinguish between following suggestions and pretending. They sound the same. In hypnosis, when you follow a suggestion, you are doing so willingly. You’re into it. You don’t notice the passage of time (as much). When you’re just pretending to be hypnotized, the session seems to drag on, and you have great difficulty cooperating what you’re asked to visualize and do. In fact, the whole thing will feel forced.
Post-hypnotic suggestion is pretty interesting stuff. It typically goes like this: While hypnotized, a person will be told “In a few seconds, I will bring you out of your hypnotized state. We will then continue our discussion on cold fusion. However, at one point during the lecture, I may say the word “light”. If you hear me say the word “light”, I want you to stand up from your desk, walk over to the lightswitch near the door, turn off the light, and say, ‘Gosh, it’s cold in here!’.” The person is then brought out of the hypnotized state. After recovering from the session (concentration’s tough after being relaxed for so long), the group conversation begins. The fun starts when the hypnotizer says “light”. I don’t have numbers or cites, but it has happened that the person has actually gotten up out of their seat and turned off the light and said it was cold.
Why it works is unknown, but it’s given weight to the divided consciouness theory of hypnosis, which is basically that when you’re hypnotized, your cognizant mind is on the shelf and your subconsciousness is on duty. When you’re brought out of hypnosis, your cognizant mind takes over, but the suggestions the subconscious side received will still spring into action if triggered.
I’ll end this way-too-long post by adding that not everyone is hypnotizable. Some people are more suggestible than others. (Though “suggestible” sounds like another way of saying “gullible”, it’s not, it’s different.) Some people have mental blocks against being hypnotized. Hypnotists have tests that can weed out these highly suggestible and stubbornly resistant folks.