Is dunking your face in a bowl of ice water each morning actually a health hack?

Mammals have two internal systems that make up the automatic nervous system. The sympathetic nervous system is activated by stress and produces the ‘fight or flight’ response, while the parasympathetic nervous system performs the opposite function, helping you ‘rest and digest’. If you’re feeling stressed or anxious, your sympathetic nervous system is responsible for the elevated heart rate and nausea. Unless you actually need to run away from a situation, it can be unhelpful and unpleasant to experience.