"Air hunger" and "alarm" are triggered by the presence of CO2 but, if done properly, the inert gas method should remove CO2 from the picture entirely - the incoming nitrogen washes out any remaining CO2 and makes up the major part of the breathable space inside the exit bag.
The Role of Carbon Dioxide (CO2)
In normal respiration, the body makes use of oxygen and produces as waste the gas, carbon dioxide. Carbon dioxide is removed from the body as we breath out. While the human body is relatively insensitive to falling levels of oxygen, it is very sensitive to any rise in the level of carbon dioxide in inhaled air. When the body detects a slight increase of carbon dioxide in the air that we breathe, a warning message from the brain alerts the person. They will be roused and may react by gasping. If a person is using a plastic Exit bag, the rise in the level of carbon dioxide within the bag may result in the person struggling to pull the bag from their head. This reaction is known as a Hypercapnic (high carbon dioxide) Alarm Response. Sleep Apnoea provides an example of hypercapnic alarm. Here the person with sleep apnea snores so heavily that they deny themselves the oxygen they need. However, it is not the lowering of the oxygen level that alarms and wakes the person, but the accompanying rise in the level of carbon dioxide. If the fall in oxygen were not accompanied by this rise in carbon dioxide, the Sleep Apnoeic would be far more likely to die. In the depressurized aircraft, the oxygen level drops but there is no accompanying rise in carbon dioxide, hence a peaceful death is the common outcome.