Yes, hypnosis is very very safe! I'm a hypnotherapist, and I have never heard of hypnosis being harmful to anyone in the many years I've worked with it.
All hypnosis is self-hypnosis, ultimately: and it's simply a form of inner focus that helps you connect with your subconscious mind in order to learn more about yourself, resolve old emotional problems, speed physical healing - the uses are endless. Many athletes use self-hypnosis to improve their performances!
We're in and out of hypnosis many times daily, very naturally: like when you space out while driving and forget to turn on the road you meant to, or when you lose yourself in a book or film.
It's actually a form of waking daydream. So safe? Yes!