Final answer:
The sympathetic nervous system division of the autonomic nervous system, which triggers the 'fight or flight' response, is activated when you experience symptoms like a racing heart and dilated pupils.
Step-by-step explanation:
When experiencing rapid heartbeat, increased breathing rate, dilated pupils, and loss of appetite, your sympathetic nervous system division of the autonomic nervous system has been activated.
This physiological response is part of the body's "fight or flight" mechanism, designed to prepare you for emergency situations.
While the sympathetic division ramps up your body's capabilities to respond to stress, the parasympathetic nervous system works to return the body to a state of rest and digest once the threat has passed.