Brian Whatcott wrote:
Nitrogen displaces oxygen, so you pass out without warning.


Material Safety Data Sheet
Gaseous Nitrogen:

SIMPLE ASPHYXIANT
Section 3 : HAZARD IDENTIFICATION
Emergency Overview:

Inhalation:
May cause dizziness.
Asphyxiant.
Can cause vomiting.
May result in unconsciousness.
May cause excitation, excess salivation, rapid breathing.
May cause headaches and drowsiness.
May cause stinging of the nose and throat.


So maybe lots of warning before passing out. But like others have said,
it only happens at extreme concentrations.