Since Influence is making a strong suggestion for the target to do something, I don't see how it would work. You can't fall asleep by deciding you want to (otherwise, the sleeping pills wouldn't be needed). I think I know where you're getting this from, with the old Hypnotist's "Sleeeeeeep" command when hypnotizing someone, but he's not actually putting the subject into a REM sleep, but it is part of the hypnosis process where he gets the subject to relax to a point of "near-sleep" where the are still conscious, but totally relaxed and open to suggestion. The Influence spell mimics this type of hypnosis, making it quite powerful, but the subject would not slip into unconsciousness. However, you do get them to the relaxed state, able to leave a post-hypnotic suggestion to forget what they saw.