Sleep, fatigue & activity during treatment — what to expect and how to help

Tiredness during cancer treatment — called cancer-related fatigue — is one of the most common side effects that children and their parents describe. It happens for several reasons working together at once. Treatment affects the bone marrow, which produces red blood cells; when red blood cell levels drop, the blood carries less oxygen and the body feels exhausted. Treatment can also cause low-grade inflammation throughout the body, disturb sleep, reduce appetite, and alter the body's normal energy cycles. On top of this, the emotional weight of a diagnosis and the disruption to a child's normal routine all drain energy. The important message is that this kind of fatigue is different from ordinary tiredness — it does not fully go away with sleep — but it can be managed with the right strategies and support.

For most children, gentle activity during treatment is not only safe but actively helpful. Research in paediatric oncology has shown that staying as mobile as appropriate — even short walks, light stretching, or slow play — can improve energy levels, support better sleep, reduce anxiety, and maintain muscle strength. The key is to match the activity to how your child is feeling on a given day, and to check with your oncology team before starting anything new. Activity should be avoided on days when your child has a fever, very low blood counts (you will be told when this is the case), or feels unwell. On better days, even ten minutes of gentle movement can make a real difference.

Children in treatment typically need more sleep than healthy children their age — and often find sleep harder to come by. Discomfort, medication side-effects, anxiety, and disrupted routines all get in the way. A child in treatment may need ten to twelve hours at night, plus one or two short rest periods during the day, depending on their age and how they are feeling. The goal is restorative sleep, not just more hours in bed. Keeping a consistent bedtime and wake-up time, making the sleep environment calm and dark, and limiting screen time before bed all help. If your child is struggling to sleep despite being exhausted, let your oncology team know — there are safe, evidence-based approaches to support sleep during treatment.

Complete bed rest for extended periods is generally not recommended unless your child is acutely unwell or your oncology team has specifically advised it. While rest is obviously important, prolonged inactivity can actually worsen fatigue over time — muscles become weaker, sleep quality drops, and mood often declines. The current approach in paediatric oncology is called 'active rest': alternating short periods of gentle movement with rest periods, rather than staying in bed all day. This means encouraging your child to do what they can, when they can, without pushing through genuine distress or exhaustion. Even sitting upright, doing light crafts, or taking a short walk counts. The balance will shift day by day, and that is entirely expected.

While some level of fatigue is expected throughout treatment, there are situations where you should contact your care team promptly. Call if your child becomes suddenly much more tired than their usual baseline — especially if it comes with pallor, breathlessness, a fast heartbeat, or difficulty walking. These can be signs that haemoglobin has dropped and a blood transfusion may be needed. Also call if fatigue is accompanied by a fever above 38°C, as children in treatment are at risk of infection. If tiredness is severe enough to prevent your child from eating, drinking, or communicating normally, that also needs prompt assessment. Your care team would always rather hear from you early than have you wait and worry at home.

For most children, energy levels improve significantly once active treatment finishes and the body has time to recover. The speed and completeness of recovery depends on the type of treatment received, how long it lasted, the child's age, and their overall health going in. Some children bounce back within weeks of finishing treatment; for others, it can take several months for energy to fully return. A very small number of children experience longer-lasting fatigue that requires targeted support after treatment ends. At CION, we walk this journey with families through the entire care pathway — not just the treatment phase. Our allied care team includes nutrition support and psycho-oncology, both of which play an important role in the recovery of energy and wellbeing.