Stress & Relaxation Response

Lesson Overview

In this lesson, we introduce the physiology of sympathetic and parasympathetic nervous system activation.


Understand the functioning of the sympathetic and parasympathetic nervous systems, and the workings of the Stress Response, Fight or Flight Response and Relaxation Response.


Explain how the nervous system responds when experiencing stress and give examples of positive triggers for the Stress Response. Describe what happens when stress is perceived to be excessive or threatening. Give examples of conditions that activate the Fight or Flight Response. Explain how the Fight or Flight Response is helpful and under what circumstance it’s harmful. Describe the Relaxation Response and practices that have been shown to initiate it.

Sympathetic Nervous System Activation

When experiencing stress, the sympathetic nervous system is activated. When stress is perceived to be excessive or threatening, a physiological reaction called the Fight or Flight Response (also called “hyperarousal” or “the acute stress response”) occurs.

  • When we experience stress, the sympathetic nervous system moves us from a state of balance to a state of preparation for action.
  • The stress response includes an increase in heart rate, breathing rate, muscle tension and elevation of cortisol and other stress hormones.
  • Positive challenges such as creating art or participating in a competitive athletic event, for example, may invoke the stress response without causing the Fight or Flight Response. (See more below.)

Stressors are External, Internal, Negative, Positive

Stressors are external or internal events that stimulate your nervous system. So if you think about it, any kind of significant change in your life is a stressor. While we tend to think of stressors being negative changes… stressors include many types of positive changes, such as getting married, having a baby, starting a new job, moving to a new city, performing on stage, and so on… And the more significant the change is (in your mind, that is—not everyone experiences the same types of changes in the same ways), the more your sympathetic nervous system is stimulated and the more “stress” you experience. – Nina Zolotow

Fight or Flight & Chronic Stress

The Fight or Flight Response

In the case of a perceived threat, the Fight or Flight (also called Fight, Flight or Freeze) Response is activated:

  • Pupils dilate.
  • Breathing quickens.
  • Digestion slows down.
  • Blood pressure increases.
  • Muscles become tense.
  • Trembling may occur.
  • The heart beats faster.
  • Blood vessels constrict.
  • Saliva decreases.
  • The parasympathetic (“Rest and Digest”) system is shut off so as to maximize the body’s response to the stress. This means digestion, restoration and healing functions are shut down.

Fight or Flight is useful as a short-term reaction because it evokes physical and emotional actions to deal with an immediate threat. If Fight or Flight is chronically triggered, the responses that are helpful in the short-term become harmful over time.

Chronic Stress

Chronic stress is known to both cause and exacerbate disease, and can lead to emotional problems such as anxiety or depression. In 2014, the Society for Neuroscience reported that 60% of Americans feel they are under a great deal of stress at least once per week.

Stress Has a Cumulative Effect

While daily stressors, like deciding what to eat for dinner, can feel simple to handle on their own, stress has a cumulative effect—even the little things and the stress they cause all adds up. Unmanaged stress can be like death by a thousand cuts and puts people at risk for numerous of health issues like anxiety, depression, headaches, sleep problems, heart disease, and weight gain… The four basic sources of stress are environmental, social, physiological, and psychological. Environmental stressors include the weather, traffic, pollution, and pollens. Social stressors include competing demands for your time, interpersonal relationships, and financial concerns. Physiological stressors include nutrition, sleeping, and health concerns. Psychological stressors include the brains interpretation of complex changes that are real or imagined as dangerous or not threats. – Ling Beisecker

Relaxation Response

  • Dr. Herbert Benson, M.D. published research in 1975 documenting what he termed the Relaxation Response, “a physical state of deep rest that changes the physical and emotional response to stress… the opposite of the fight or flight response.”
  • Initiating the Relaxation Response corresponds with activation of the parasympathetic nervous system.
  • It switches off the stress response and its associated increase in heart rate, blood pressure, mental alertness and muscle tension.
  • When the Relaxation Response is activated, so too are the bodily systems that were shut down from the Fight or Flight Response, including digestion, elimination, growth, repair and reproduction.
  • Meditation and relaxation activities have been shown to initiate the relaxation response.
  • Often, the positive effects of yoga are associated with this effect on the nervous system. (See Yoga’s Impact on the Nervous System & Stress for more detail.)

Nervous System As Our Communicator with Spirit

The nervous system is our communicator with Spirit, our connection with the inner worlds, a gateway between the physical and spiritual… An agitated nervous system fails to receive the Spirit’s guidance, just as a warped antenna cannot receive television signals properly.   The nervous system feels joy and sorrow, initiates laughter and tears.  However, when under stress, it fumbles through its job, and so do we.  In our yoga practice and in life, we must protect our nervous system and ensure that it lives in a state of equanimity. – Aadil Palkhivala


Biological & Psychological Response

The Stress Response is a biological and psychological response experienced on encountering a threat that we feel we do not have the resources to deal with… Our body judges a situation and decides whether or not it is stressful. This decision is made based on sensory input and processing (i.e. the things we see and hear in the situation) and also on stored memories (i.e. what happened the last time we were in a similar situation). If the situation is judged as being stressful, the hypothalamus (at the base of the brain) is activated. – 

Different Types of Stress, One Stress Response

Interestingly, despite all the types of stressful situations a person can be in (standing on your head, running away from a lion, finishing those reports by 5 o’clock) the nervous system has just one stress response.  The specific thoughts you have may differ, but the brain regions involved, and the physiological response will be the same.  The physiological stress response means an increase in heart rate, breathing rate, muscle tension and elevation of cortisol and other stress hormones. – Alex Korb

Bodies are Slow to Recover from Fight or Flight

Effects from a fight-or-flight response take a long time to wear off. Muscles that have tensed are left shortened and do not automatically go back to their former length. They remain relatively short and tense until the reflex is reset by a relaxing experience, like the gentle, conscious stretching that occurs during a massage or a yoga session. Muscles aren’t the only part of the body slow to recover from a fight-or-flight reaction. Stress hormones remain in the bloodstream for quite a long time, and more may be released in response to memories of the danger. – Roger Cole

Chronic Stress Can Lead to Emotional Problems

There is agreement that chronic stress can cause a whole range of emotional problems, including both depression and anxiety… When you’re in stress mode, your thoughts narrow and become limited to fight or flight strategies, while when you are calmer, your thoughts are more expansive, and therefore include a much wider range of possibilities… One of the common effects of an overactive sympathetic nervous system is insomnia… sleep deprivation triggers accelerated mental decline. – Nina Zolotow

The Freeze Response

Most of us are familiar with the term “fight or flight” as a response to stress. However, there is another response: the freeze response…Being physically, mentally, and emotionally immobilized by your consternation permits you not to feel the harrowing enormity of what’s happening to you, which in your hyper aroused state might threaten your very sanity. In such instances… endorphins… function as an analgesic, so the pain… is experienced with far less intensity… such “paralyzing” psychological phenomena as phobias, panic attacks, obsessive-compulsive behaviors, and various anxiety states can frequently be understood as symptoms of a freeze response that never had the chance to “let go” or “thaw out” once the original experience was over. – Beth Gibbs

The Freeze Response & The Natural Cycle

The theory is that when the wild animal (humans being an animal) are scared, they run. When they’re angry, they fight. When neither of those is gonna work, they freeze and play dead. When the danger has passed, they shake it off and move on with their lives. Much of modern culture trains us to be stoic, to keep a stiff upper lip, to internalize our struggle and not appear “weak” or “emotional.”… Woody Allen joked that “Oh, I don’t get angry. I just grow a tumor.” Resilience is often confused with stoicism, when in fact stoicism is a recipe for being stuck in a never ending cycle of a stress feedback loop: the stress cycle is interrupted by our efforting, resistance, or over-thinking, and gets stuck like a broken record… we can inhibit anger, fear, tears, sadness, or grief from fully expressing by holding our breath, keeping ourselves busy, or constant media exposure. In Somatic Experiencing sessions, I’ve seen time and again the healing nature of giving oneself over to this natural biological cycle of the stress response. – Sound Mindfulness Group, Resilience