When we sleep we enter into a Rapid Eye Movement state where we rerun the events of the day and change them from being an emotional memory into a narrative memory – one that we have control over. Either we replay the events of the day, or we substitute the event for a dream containing the same emotional response pattern the mind wants to discharge. In hypnosis, we enter into that same trance state – a state fundamentally necessary for our wellbeing. We then have access to the subconscious mind, the place where response patterns are stored. With that, the brain works enormously hard to come up with a solution to a problem that we have decided we would like.
Nature rarely gives us something which we have no use for. Early man and woman would have been at their most vulnerable when asleep. Therefore, the reward must have been great.