Re drowning: to my understanding, doing this prior to submersion will cause vasoconstriction - which, yes, will lead to cerebral hypoxia, but this will be reversed upon activation of the compensatory response, causing one to wake up. The problem here is that there is too much residual O2 despite the transient cerebral hypoxia due to vasoconstriction of cerebral blood vessels. This is why I plan to use N2O before submerging my head underwater.
Re hanging: I suspect that one might regain consciousness. This would seem highly dependent upon technique and physiology, that is, whether it would take 10 seconds for unconsciousness to occur (assuming one had not fainted prior) or 60 seconds. Furthermore, doing this might cause one to fall into the noose in the wrong way.
Re jumping: this could work if you are falling, say, 1000+ feet with no obstacles on the way down, but otherwise it is probably unwise, as it will compromise your ability to plan the jump and position yourself (if you are able to do so, as admittedly, this can be quite difficult due to SI kicking in).