I taught myself self-hypnosis to a degree in 6th grade. I have since read a couple of books and had two three day formal training days.
You have to agree with it and not fight it.
So once I was in Houston and the granddaughter of the most notable hypnotist of the last 100 years, Dr. Milton Erickson, was in attendance. She had never been hypnotized, but came there to find out more about her internationally known Grandfather, who had passed away before her birth. So on the second day, they randomly pair her and I together, and I was to induce a trance and prove it by doing what's called hand levitation. It worked.
I attended a lecture by someone who worked at MD Anderson and they said they use hypnosis every single day Monday through Friday for pain management.
It truly is under utilized. You won't do things that you morally disagree with. Actually, we are in a sense hypnotize several times a week, such as driving down an empty road, staring to the distance seemingly daydreaming. Being in hypnosis is nothing like being in sleep. It's more like having a razor sharp focus on one particular thing.
While getting my doctorate we had to undergo bio feedback, the idea is to make your right pinky warmer than your left pinky and the tones the equipment admit it would let you know whether it was working. I did eight sessions and every time there was a significant difference in temperature. I'm a skeptic, but there's too much evidence that hypnosis works as well as bio feedback. You've all heard of the mind-body connection. It is very real.
With most certifications, you have to agree not to do stage acts. That can make fun of people and it hurts the credibility of hypnosis.
I concur that some people are much more susceptible to hypnosis and there's a technique that you can use to determine who those people are if you're in front of an audience.
Edit: A speaker from MD Anderson said someone trained in self hypnosis had a partial mastectomy done without pain medication during the procedure.