Alarm Stage:

Alarm stage, the first stage of the fight-or-flight response (FFR) — one of three stages in the General Adaptation Syndrome (GAS) theory of FFR — when the body’s systems are faced with a stressor. See also Resistance and Exhaustion Stages. Alarm stage:

• Alarm signal is sent to the brain’s command and control center (amygdala). It perceives danger and sends a distress signal via nervous system to the hypothalamus, becoming another command center.
• Hypothalamus signals body through autonomic nervous system (controls involuntary functions) and activates sympathetic nervous system (SNS). SNS triggers adrenaline to rush into bloodstream, providing burst of energy in well-orchestrated, near-instantaneous physical changes.
• As adrenaline surge subsides, hypothalamus activates second stage of stress response system: HPA axis—hypothalamus, pituitary gland, and adrenal medulla—relies on hormonal signals to keep energy surging and prime the body to fight or flee to safety.
• If danger continues, hypothalamus and pituitary gland release other hormones—adrenal medulla releases cortisol—keeping the body revved up and on high alert.
• After initial shock, body’s parasympathetic nervous system (PNS) actslike a brake to calm down and  repair by lowering cortisol levels, blood pressure, and heartrate. Body still remains on alert until danger passes, usually 20-60 minutes.