I use sleep hypnosis all the time. Before bed, we are in Theta brainwave state. This is where we are as babies and up until a certain age, like four? I can't remember. What I learned is that Theta brain state is where we absorb what's going on around us, take it in, and the brain hears it even if we are on the verge of sleep or in "baby-age-state".
Theta is the most suggestible state, and it's where we are when drifting off to sleep (one can research this easily). Most sleep hypnosis videos on Youtube.com begin with a few minutes of suggesting that one get comfortable, think about the countdown or whatever the speaker is saying, and then moving into "deep relaxation." Many are not religious (though many are), and all really only want to support the change the person listening is seeking.
I listen to the whole video to make sure they aren't suggesting I go kill someone, ha ha. (Seriously, you never know.) However, I now listen to a couple of individuals on a regular (nightly) basis. There are great "getting over codependency" hypnosis videos (you don't watch the video, obviously, as your eyes are closed). There are many for getting over someone, detaching, healing the inner child, and any other topic you can think of. Sometimes, I put one on in the afternoon after grading papers or being stressed, and it calms me down, relaxes me, and reminds me of my successful work of late.
One thing I like I that the videos are free. Some are 20 minutes and some are hours long. I have listened to some for hours while sleeping before. There was a good one I found where the guy helps me find "the answers" I am looking for. It was super cool. The people who do this for real are gentle, reaffirming, helpful, caring, and really want to help people, which one can hear in the ways they tell the listener what the listener needs to hear. The listener feel loved.
The codependency hypnosis I have been using tells me that we often have parents who cannot raise us correctly, that it's not our fault, that we can overcome, and so on...the speaker acknowledges the pain and offers ways to overcome codependency. The first time I listened I cried a bit because I felt understood for the first time.
I have been listening to hypnosis videos for about four months now, and I truly believe they help me and have helped me. I also listen to "I am" affirmations. When I was a Christian, these made me feel inadequate because I had been taught my best efforts were "dirty rags" compared to Christ. Affirmations went against what I was taught. However, they have really helped me to know me better, to feel better about myself, to love myself, and to stop putting myself below others.
I tell people to go to Youtube.com, search through the videos, listen to some to see what voices you like, what background music you like, and what suggestions you feel will help you the most while in Theta brain state. Then, do it!! What can it hurt? It's my opinion that anything that helps reinforce what we are learning and doing is a very good thing.