Living with AS fatigue: why you're not just tired

One of the conversations I have most often with people who have recently been diagnosed with AS goes like this: 'I know the back pain is from the AS. But why am I so exhausted all the time? Is that just the medication? Am I depressed? Am I just not coping?'

The answer is: no. The fatigue is the disease.

What AS fatigue actually is

AS is a systemic inflammatory condition. The inflammation is not confined to your sacroiliac joints and spine — it affects the entire body. And systemic inflammation has a well-documented effect on energy levels that goes far beyond what you would expect from the pain itself.

When your immune system is chronically activated, it produces inflammatory cytokines — proteins that act as immune system messengers. Two of the most significant for AS are TNF-alpha and IL-6. These cytokines directly drive fatigue. IL-6 in particular activates the brain's 'sickness behaviour' response — a set of symptoms including profound fatigue, reduced motivation, social withdrawal, and cognitive dulling that is basically your body trying to redirect energy toward fighting the inflammation.

This is not tiredness. It is your immune system consuming resources. It cannot be fixed with an early night. It cannot be pushed through indefinitely without a cost.

What makes it different from normal tiredness

Normal tiredness improves with rest. AS fatigue often does not — or improves only partially. You can sleep eight hours and wake up feeling like you have barely slept at all. You can sit down for a rest and feel worse after twenty minutes of inactivity than you did before.

The combination of pain and inflammatory fatigue is particularly cruel. The pain disrupts sleep. Disrupted sleep worsens the inflammatory fatigue. The fatigue makes everything harder to manage, including the pain. It is a cycle with no obvious entry point.

The cognitive dimension is also real: brain fog — difficulty concentrating, forgetting words, losing track of what you were doing — is a recognised feature of inflammatory fatigue. It is not 'just tiredness' and it is not 'just getting older.'

Energy management — what pacing actually means

'Pacing' is a word that gets used a lot in chronic illness management. It sounds passive — like you are just going slowly. What it actually means is learning to manage energy as a finite resource rather than something you can borrow against indefinitely.

The crash-and-burn cycle is what happens without pacing: you have a good day, you do all the things you have been putting off, you exhaust yourself, and you spend the next two days paying for it. Sound familiar?

Pacing means doing less on good days than you feel capable of, in order to have more reserves across more days. It means stopping before you hit the wall, not when you hit it. It means building in rest proactively rather than reactively.

This is genuinely one of the harder skills to learn. Productivity culture makes people feel guilty for not doing everything they can while they feel okay. You have to unlearn that.

Sleep and AS fatigue

Sleep quality is a major driver of daytime fatigue, and AS makes good sleep hard. The inflammatory pain is characteristically worst at night and in the early morning — it is one of the diagnostic criteria, actually. People with AS regularly wake in pain in the small hours. The sleep they get is often fragmented and unrestorative.

Things that help: taking NSAIDs before bed (the anti-inflammatory effect carries through the night), a firm-to-medium mattress that supports spinal alignment without creating pressure points, keeping a heat pad beside the bed for middle-of-the-night pain, and maintaining a consistent sleep schedule even on weekends.

Sleep in AS is worth treating as a medical issue, not just a comfort issue. Discuss fragmented sleep with your rheumatologist. There are interventions — including Cognitive Behavioural Therapy for Insomnia (CBT-I), which has better long-term evidence than sleeping pills — that can help.

Communicating fatigue to people who don't have it

This is hard. 'I'm exhausted' is something everyone experiences, and it is difficult to convey that what you experience is qualitatively different from a bad night's sleep.

What sometimes helps: being concrete rather than general. Not 'I'm tired' but 'I'm running on about 30% today and I need to protect that for work.' Not 'I can't come' but 'I'm managing a flare and I need to save my energy — can we reschedule for next week?'

The people who matter will learn to read this. The ones who don't will always think you're making excuses, and that is ultimately their limitation, not yours.