This is what happens in a hypnotherapy session:
If you haven’t already discussed how the session is supposed to help you, you discuss it with the hypnotist. E.g., reduce eating. She helps you formulate the message you want to tell yourself.
Then she has you do some relaxation exercises.
You are in a comfortable chair, your eyes are closed, you do a couple of deep relaxation breaths. You do muscle relaxation: head, face,jaws, neck, etc, etc. Mixed with that is the recurring e message you are more and more relaxed.
Then she has you do some type of count-down exercise and reminds you that with every increment you are getting more relaxed. Sometimes the countdown is the alphabet, sometimes something else. Then there is usually some type of imaginary step climbing; each step brings more relaxation. Then you imagine yourself in a comfortable place, you are very relaxed. Then she has you visualise being successful: passing by food; taking small portions and being satisfied; drinking lots of water, all the things you wanted to tellyourself. She helps you visualize them. Then she slowly brings you out of this complete relaxation and you open your eyes.
At all times you are aware of what is going on. Your critical faculties are at work; if something sounds wrong in a non-hypnotic state, it sounds wrong under hypnosis. Hypnosis doesn’t work if you don’t want it to .
Free will is not an issue; only in comic books can someone be hypontised to do what they don’t want to do.
Some people hypnotize easier than others, but it only ever works if you want it to.
There are some goofy practioners, just like there are goofy chiropracters. You can find plenty that have alternate spiritualities. But there are Catholic ones and plain old practical ones as well. Find one without some spiritual agenda, and you’ll do well.
I suggest that other posters inform themselves on the subject rather than relying on assumptions and rumors.