The Window of Tolerance: What It Is and Why It Matters

If you’ve ever wondered why some days you can handle stress with relative ease and other days even small challenges feel overwhelming, the concept of the window of tolerance offers a powerful explanation. 

First introduced by psychiatrist Dr. Dan Siegel, the window of tolerance describes the range of nervous system activation within which we can function effectively whether that be emotionally, cognitively, and relationally (Siegel, 1999). Inside this window, we are better able to stay present, flexible, and connected. Outside of it, our nervous system shifts into survival responses designed to protect us. 

Understanding the window of tolerance helps move us away from self-judgment and toward a more compassionate, physiological understanding of our experiences. 

A Simple Explanation of the Window of Tolerance 

Think of your window of tolerance as a band of capacity. When life stays within that band, stress feels manageable even when things are challenging. When stress exceeds that capacity, the nervous system shifts out of regulation. 

The size of this window is not fixed. It can widen or narrow over time depending on factors such as chronic stress, trauma history, physical health, pain, relational safety, and available support (Ogden et al., 2006). 

This framework reminds us that overwhelm is not a personal failure, it’s a signal that the nervous system’s capacity has been exceeded. 

The Autonomic Nervous System: What It Regulates 

The autonomic nervous system (ANS) governs the body’s automatic processes, or the functions that occur without conscious effort and are essential for survival. These include heart rate, breathing, digestion, blood pressure, immune response, hormone regulation, muscle tone, temperature control, and pain perception (Porges, 2011). 

Rather than responding to logic or willpower, the ANS continuously scans for cues of safety or threat. When safety is perceived, the body can prioritize repair, connection, and growth. When threat is detected, the system shifts toward protection. 

The ANS is made up of two primary branches that work together to support this process: the sympathetic and parasympathetic nervous systems. 

Sympathetic and Parasympathetic Systems: Mobilization and Conservation 

The sympathetic nervous system mobilizes energy. It increases heart rate, sharpens attention, and prepares the body for action. This system supports fight and flight responses and is essential for responding to stress, challenge, and danger. 

The parasympathetic nervous system conserves energy. It slows heart rate, supports digestion, and facilitates recovery and repair. While often associated with rest, it can also contribute to shutdown when overwhelm becomes too great. 

Healthy regulation depends not on staying in one state, but on the nervous system’s ability to move flexibly between activation and rest (Siegel, 2020). 

Inside and Outside the Window of Tolerance 

When we are inside the window of tolerance, the nervous system can shift fluidly between sympathetic and parasympathetic activation. We may feel energized at times and calm at others, but we remain present, responsive, and connected. 

When stress exceeds capacity, we move outside the window. 

• Above the window, the sympathetic system dominates, leading to hyperarousal (fight or flight). 

• Below the window, the parasympathetic system may shift into a protective shutdown state known as hypoarousal (freeze). 

These states are not choices or personality traits—they are automatic survival responses. 

Rest and Digest vs. Hypoarousal: Why the Difference Matters 

A common misconception is that all parasympathetic states are restorative. In reality, there is an important distinction between rest-and-digest and hypoarousal. 

Rest-and-digest occurs when the nervous system perceives safety. The body can digest food, regulate hormones, repair tissues, and engage socially. This state supports healing and resilience. 

Hypoarousal, however, is a protective shutdown response that occurs when stress or threat feels overwhelming. While parasympathetic-dominant, it is not restorative. It is often associated with numbness, disconnection, low energy, and reduced emotional access (Ogden et al., 2006; Porges, 2011). 

This distinction matters because many people attempt to “rest” while their nervous system is actually in shutdown. True restoration requires safety, not just stillness. 

How Stress, Trauma, and Chronic Pain Narrow the Window 

Chronic stress, unresolved trauma, and ongoing adversity can narrow the window of tolerance, meaning it takes less stimulation to push the nervous system into survival states. 

Research shows that prolonged autonomic dysregulation can sensitize the nervous system, increasing baseline activation or shutdown (Porges, 2011). This is especially relevant for individuals living with chronic pain, where persistent nervous system threat responses can amplify pain perception and emotional distress (Fisher et al., 2019). 

Over time, this reduced flexibility can make everyday life feel exhausting or overwhelming, even in the absence of immediate danger. 

Why the Window of Tolerance Is Empowering (Not Diagnostic) 

The window of tolerance is not a diagnosis or a measure of mental health. It is a framework that normalizes nervous system responses and places them in context. 

Rather than asking, “What’s wrong with me?” it invites the question, “What support does my nervous system need right now?” 

The most hopeful part of this model is that windows can expand. With safety, supportive relationships, and consistent regulation practices, the nervous system can learn that it no longer has to remain in survival mode. 

In the next posts in this series, we’ll explore how to gently expand the window of tolerance and why co-regulation, the stabilizing presence of others, is one of the most powerful tools for nervous system health. 

Leanne Sudbeck, MSW, SWLC 

References 

Fisher, J., Murray, K., & Bundy, A. (2019). Sensory processing, autonomic nervous system functioning, and chronic pain. Frontiers in Integrative Neuroscience, 13, 1–11. 
https://doi.org/10.3389/fnint.2019.00058 

Nagoski, E., & Nagoski, A. (2019). Burnout: The secret to unlocking the stress cycle. Ballantine Books. 

Ogden, P., Minton, K., & Pain, C. (2006). Trauma and the body: A sensorimotor approach to psychotherapy. W. W. Norton & Company. 

Porges, S. W. (2011). The polyvagal theory: Neurophysiological foundations of emotions, attachment, communication, and self-regulation. W. W. Norton & Company. 

Siegel, D. J. (1999). The developing mind. Guilford Press. 

Siegel, D. J. (2020). The developing mind (3rd ed.). Guilford Press.