Where one achieves orgasm, by deliberately cutting off their own air supply. Also known as 'Breath Play' or 'Erotic Asphyxiation'.
While generally done in a solitary environment, the risks are enormous, for potential death.
Many believe some deaths, labelled as suicide, where in fact attempts at Asphyxiophilia, or Breath Play, that went wrong.
World's Best Dad starring Robin Williams deals with this topic as well, where a worst case scenario happens.