When we sleep naturally, we "fall" asleep. We don't "try" to sleep, or force ourselves to sleep. Once you're in a vicious circle of trying to sleep and not being able to, it can be very difficult to escape. Hypnosis resets your natural sleep ability, calming your conscious mind and letting your unconscious mind get on with its job.
Sleep habits are very responsive to hypnotic approaches, partially because hypnosis mirrors the natural process of falling asleep. Hypnosis will help you cut through worrying thoughts, anxious feelings, and anything else that's getting in the way of your shut eye.