Hypnotizing myself-is this is a good or bad idea?

I have a big swim meet tomorrow and on Saturday, and there is a cut time I'm trying to get. I have been practicing really well and feeling great about myself in practice, but for some reason when it comes to meets I begin to doubt myself and feel negative. I've been listening to this hypnosis visualization tape to try and help with that, and it seems to work for practice but, I want to be extra sure for this meet, so a friend suggested that I put the tape on repeat and play it while I sleep, quiet enough for me to be able to fall asleep, but loud enough just so that my subconscious takes it in while I'm sleeping. I had doubts about this because at the end of the tape, the man narrating it tries to take you out of the relaxed state your in, and seeing as the tape is only 15 minutes long, I'm worried that if I put it on repeat all night I'll wake up every 15 minutes, but if I'm deeply sleeping, that shouldn't happen. Do you think my friends' suggestion is a good idea? And if not, what should I do to mentally prepare myself and be confident for my races?