My guess is: it feels nothing if you actually manage to break the neckbone, you just detach the brain from the body. If you don't, and then die by bone breaking suffocation or hypoxia, it's a fucking hell, this is the majority of cases.
"In most cases, death by hanging is caused by brain ischaemia which develops because of compression on the airways and blood vessels of the neck and sometimes reflex cardiac arrest occurs due to vagal inhibition created by pressure on the carotid sinus. Occasionally, death may occur as a result of mechanical asphyxia due to obstruction of the airways with the swallowing of the glottis and tongue directly into the pharynx caused by restriction of the neck. However, these mechanisms of hanging should not be considered separately from each other as it is thought that the inhibition of respiratory and circulatory functions together result in acute brain ischemia leading to death [
1,
6]. Research into determination of the origin of death as a result of hanging, which is a frequently seen method of suicide, is of great importance. In addition to death by hanging generally being suicide, cases of accident and murder have also been reported [
7-
9]. "
Background: Death by hanging occurs as a result of the tightening of a cord around the neck with the effect of body weight. Although generally seen, it is not always necessary for ..
www.alliedacademies.org
For the record, on wikipedia there is a table of drop/rope lenght used for capital executions.
en.wikipedia.org