Can self hypnosis help post traumatics stress syndrome?

Exposure. While medications may help treat symptoms associated with ptsd, exposure and response prevention therapy is likely to have longer lasting and enduring effects. This must be done with a trained professional. I would not recommend self hypnosis to anyone who has not gone through exposure therapy first. Ptsd is very treatable and you may find it very uncomfortable.
Possible. Self hypnosis can be quite effective in modifying your stress response, but it would be better and safer to cocurrently work with a professional such as a psychotherapist or a psychiatrist.