Most people would translate this as 'nightmare' in English when in fact it is slightly different. Bangungot or Nabangungot refers to an event or happening wherein a person experiences during his/her sleep a cursed dream, usually attributed to a ghost, and then to unfortunately never wake up. Think of it like a ghost-like figure coming to you at your sleep and suffocating you with her breast. FYI, the correct translation for nightmare in English is 'masamang panaginip' which literally means bad dream. Bangungot includes death, masamang panaginip does not (usually).