You have to remember that suicide is damaging your brain to the point where it can no longer function. Every single method is going to carry with it some risk of adverse effects if you survive, including brain damage.
If you deprive your brain of oxygen long enough, it will start dying. If you are then resuscitated after that, you will have to deal with parts of your brain being dead. The extent of the damage just depends on how long you were oxygen deprived and how well your brain can recover from the damage it has received.