Some people think that hypnosis can bring back really bad memories of past lives or even events that you were not present for. It can help in a lot of ways and this is basically what it does:
It reduces the mind down to a state where it will accept anything it is being told as true. Eg you are a chicken. This means the mind can be 'reprogrammed' into doing or not doing something. As long as you 100% believe that the hypnosis will work then there is a strong chance of it suceeding. If not, then it might not work. Hope that helped!

VERY important. Go to a reputable hypnotist - one who is registered with a reputable association and not just someone who can do it or is a stage hypnotist. It totally relaxes your body but your brain is alert. You have discussed whatever the problem is with your hypnotist first so when you are 'under' he/she will make suitable suggestions to your subconscious. If you go back to painful memories it helps them come out harmlessly and you feel fine afterwards. Find a good practitioner though.

Hypnosis works by bringing a person into a peculiar state of consciousness with reduced peripheral awareness accompanied by strictly focused attention.

While a person are in this state they are highly receptive to be influenced by suggestion directed at a person.

If you try to bring back past memories, be careful and remember that you can bring unwanted memories to surface.

If a person in unable to undergo hypnosis it has more to do with having a critical mind, if a person wants to be hypnotized, it is very important that he/she keeps an open mind and trust whoever is hypnotizing.