Grief is an HPA axis story, not just a heart story

The five stages of grief are a comforting fiction, a neat flowchart for an experience that is messy, circular, and profoundly physical. Your body registers a profound absence as a threat on par with a physical injury, triggering a long-duration, system-wide alarm. This is grief: a physiological event, not a tidy sequence of emotions to be checked off a list.

You are functioning. You make it to work, reply to emails, and stand by the coffee machine performing a passable version of your former self. But the world feels muted, as if you’re watching it through a dusty window. The colour has been turned down. Familiar words hover just out of reach, like a file that will not load. A simple head-turn makes the room spin. You catch every cold that goes around the office, and the fatigue is relentless, a gravitational pull that no amount of sleep seems to touch. You’re offered advice: talk it out, take a trip, try a new supplement. The feeling is not sadness in the way people mean. It’s a heavy, slow, offline state—the physical readout of a nervous system stuck in a crisis it cannot resolve.

Grief is a long-form HPA axis event

Your body's central stress response system is the hypothalamic-pituitary-adrenal (HPA) axis. In a typical stress scenario—a missed deadline, a difficult conversation—it fires up to release hormones like cortisol, mobilises energy, and then powers down once the threat has passed. The system is designed for sprints.

Grief is a marathon. The loss registers as a persistent, long-duration signal of threat and a radically changed environment. Your HPA axis does not get the 'all-clear' signal to stand down. This results in chronically elevated cortisol. For years, I viewed grief primarily through a psychological lens, as a narrative problem to be solved with insight. I was wrong. Grief is a hardware problem before it's a software problem; the body’s operating system has been fundamentally altered by the loss.

This sustained cortisol elevation systematically disrupts other core processes. It interferes with your sleep rhythm, often causing the classic 3am wake-up as your body gets a mistaken 'time to face a threat' signal. It destabilises blood sugar, leading to afternoon energy crashes and intense cravings for high-energy food. It also impairs the function of the hippocampus, the part of your brain responsible for forming new memories and retrieving old ones. This is a key reason why grief can feel so disorienting; your brain's ability to create a coherent narrative of 'before' and 'after' is biochemically compromised. The past feels both impossibly distant and painfully immediate, while the present struggles to register at all. The classic 'tired but wired' state is the signature of a body primed for a threat that is internal, abstract, and has no end date.

Related anchors: sleep anchor · gut-immune anchor · wired-tired anchor

Chronic inflammation is the static in the signal

A nervous system stuck in high-alert mode eventually triggers a state of low-grade, chronic inflammation. Your immune system, under constant orders from the overactive HPA axis, begins to release a steady stream of pro-inflammatory messengers called cytokines. These are the exact same molecules your body produces when you have the flu. They are responsible for a physiological state called 'sickness behaviour'.

This is an intelligent, coordinated shutdown sequence. Sickness behaviour includes fatigue, brain fog, aches and pains, loss of appetite, and a profound desire to withdraw from social contact. It is your body's non-negotiable attempt to conserve energy and dedicate all available resources to managing a crisis. When you are grieving, your body believes it is managing a five-alarm fire that never goes out. I often hear clients describe the physical ache of grief with a sense of apology, as if it’s not real. The ache in your joints is as real as any flu; it’s the physical signature of an immune system working overtime without a clear enemy to fight.

This state is highly adaptive for fighting off a short-term infection. It forces you to rest, which is exactly what the immune system needs. But when the 'infection' is an abstract loss with no clear endpoint, sickness behaviour becomes a chronic condition. You are trapped in a biological script for an acute illness that has become your new normal. These inflammatory messengers create a kind of biological static, drowning out the signal of the present moment with the noise of an internal emergency broadcast.

The biology of social withdrawal

The urge to withdraw from the world during grief is a physiological reflex, a deep, ancient energy-saving mode. Your system, already managing the massive overhead of chronic HPA axis activation and inflammation, makes a brutal but logical calculation: social interaction is too expensive. It requires parsing facial expressions, modulating your own voice, holding context—all metabolically costly tasks. To conserve fuel for core functions, the body simply cuts power to the social engagement department. This are a biological budget cut.

The world can seem muffled, distant, and unreal. Your limbs feel heavy. In this state, even the sound of a friendly voice can feel abrasive, like a bright light in a dark room. I find this is the part of grief that friends and family struggle with the most. They offer connection as a cure, but to a system in deep conservation mode, that offer lands as another demand—another withdrawal from an already overdrawn account.

This biological retreat is frequently misinterpreted as a personal rejection or a symptom of depression. Well-meaning advice to “get out there” or “lean on your friends” lands as an impossible demand on a system that has deliberately gone offline. The desire for connection may still be there, but the capacity to enact it is unavailable. The body is prioritising bare-bones survival over social bonding.

Common Questions

Why does grief feel like a physical illness?

Because at a cellular level, it is. The chronic stress of grief triggers the release of inflammatory molecules called cytokines, the same ones that cause 'sickness behaviour' when you have the flu. This is your body's intelligent, if painful, strategy to conserve energy. It leads directly to the fatigue, brain fog, body aches, and social withdrawal that define both sickness and deep grief.

Is the brain fog from grief permanent?

The brain fog from grief is a temporary state. It reflects a brain conserving energy while under immense physiological load. This symptom of your system's current capacity resolves as the nervous system begins to regulate. As the inflammatory load decreases through rest, gentle movement, and proper nourishment, cognitive function returns to its baseline.

Will exercise help or hurt my grief recovery?

It depends entirely on the type, intensity, and timing. Pushing through a high-intensity workout can add more stress to an already overloaded system, making things worse. Gentle, restorative movement like walking in nature, slow stretching, or tai chi can help regulate the nervous system, process stress hormones, and gently reduce inflammation without demanding more energy than your body has to give.

Why do I feel so disconnected from people trying to help?

Your nervous system has entered a state of radical energy conservation. Faced with the huge metabolic cost of chronic stress and inflammation, it makes a pragmatic decision to cut power to non-essential activities. Social engagement—reading cues, making conversation, managing emotions—is incredibly energy-intensive. The feeling of disconnection is your biology prioritising core survival functions over social bonding. It's not a rejection of help, but a system-wide power-save mode.

Closing

Recognising the physiological reality of grief is the first step. The next is to give your system the specific support it needs to navigate this state without demanding that it perform a recovery it is not ready for.

• For a deep dive into the mechanisms of regulation, the self-paced course, The Kokorology Foundations is the place to start.
• If you need individual support to map your own nervous system's response, you can learn more about 1:1 Sessions with Sabin.
• For free, weekly insights on nervous system health delivered to your inbox, join The Dispatch.

TL;DR

Grief is a long-duration physiological state, more than an emotional one. Your body registers a major loss as a chronic threat, keeping the central stress system (the HPA axis) activated and cortisol levels high. This triggers low-grade inflammation, producing physical symptoms like fatigue, brain fog, and immune suppression—a state known as sickness behaviour. Effective support means addressing this physiological load directly with nervous-system tools, rather than just trying to process the story of the loss.

Sources

• O’Connor, M-F. (2019). Grief: A Brief History of Research on How Body, Mind, and Brain Adapt. Psychosomatic Medicine, 81(8), 731–738.
• Slavich, G. M. (2020). Social safety theory: a new systems approach for understanding stress, inflammation, and disease. Metabolism, 111S, 154341.
• Freudenberger, H. J. (1974). Staff Burn-Out. Journal of Social Issues, 30(1), 159–165.
• Lieberman, M. D., Eisenberger, N. I., Crockett, M. J., Tom, S. M., Pfeifer, J. H., & Way, B. M. (2007). Putting feelings into words: affect labeling disrupts amygdala activity in response to affective stimuli. Psychological Science, 18(5), 421-428.