This is just folklore. Your body won't just take over and attempt to free itself.
What happens is cerebral hypoxia, or cutting off a significant amount of blood supply to your brain prevents new memories from forming, which is to be expected if you think about it. The brain needs fuel to operate, which comes in the form of oxygen and glucose. When you starve the brain of these things, certain functions are not able to operate. Forming new memories is then effected.
If you are unsure of ctb or have doubts, what happens is you will try to escape the predicament you are in because subconsciously you have these doubts. Especially with partial hanging attempts. After consciousness is lost, the body goes through mild generalized convulsions. The body also will straighten the limbs and then retract them. In a partial attempt, where part of your body is still in contact with the floor, straightening the legs can lead to relieving some of the critical pressure on the carotids, which restores blood flow to some degree and this provides the brain enough fuel to regain consciousness.
Partial hanging requires a lot variables to be accounted for, and any neglect of them is going to lead to failure. Mostly, there is only one partial position that exerts the necessary pressure that is required to block the carotid arteries. This is why so many people try it and get the exploding head feeling - their jugulars are blocking the return of blood out of the brain while the carotids are continuing to pump blood in to the brain.
