Physiological arousal precedes one's feeling.
This means that the body's nervous system is activated before one is consciously aware of feeling anything.
The autonomic nervous system is responsible for this arousal.
The autonomic nervous system is split into the sympathetic and parasympathetic nervous systems.
The sympathetic nervous system is responsible for the "fight-or-flight" response.
The parasympathetic nervous system is responsible for the "rest-and-digest" response.
Physiological arousal can be caused by many things, including emotions, exercise, and drugs.
Arousal is necessary for all emotions, even positive ones.
Too much arousal can lead to anxiety, and too little arousal can lead to depression.
Arousal can be measured by changes in heart rate, respiration, and skin conductance.