Feeling Run-Down? 6 Signals Your Body Might Send You
Rebecca Miller
By the time a sore throat, runny nose or cough appears, an infection may already have begun before these more familiar symptoms become noticeable.
The changes can be subtle at first: unusually low energy, a restless night or a workout that feels harder than usual. You might put them down to a busy week or poor sleep, without realising they could accompany the early stages of an infection.
Wearable devices have made it easier to track measurements such as resting heart rate, sleep and activity over time. Researchers are investigating whether changes in these everyday measurements can help identify infections before people report symptoms.
Some findings are promising. In one study of people with COVID-19, researchers observed changes in heart rate, daily steps or time asleep, sometimes before reported symptoms began. However, the study used retrospective data and included only 32 infected participants. It does not establish that a smartwatch can reliably diagnose an infection.1
These changes are not a diagnostic checklist. Some are symptoms of illness themselves rather than warnings that appear beforehand, and many can occur for other reasons. A change from your usual baseline is something to notice - not proof that you’re getting sick.
This guide explores six changes that can accompany the early stages of a respiratory infection, what science can tell us about them and practical ways to look after yourself.
1. You feel more tired than usual
Waking up feeling unrefreshed, struggling to concentrate or finding everyday tasks take more effort than they normally would?
Fatigue can accompany an infection, and the immune response can contribute to that feeling of tiredness. When the body responds to an infection, immune signalling molecules help coordinate its response and communicate with the brain, influencing how you feel and behave.2
But tiredness is also associated with plenty of other things, from poor sleep to stress, and an unexplained dip in energy does not tell you what is causing it or whether an infection’s developing.
What to consider: Pay attention to how you feel compared with your usual baseline. If your energy has dipped unexpectedly, consider easing back on strenuous activity, prioritising sleep and allowing yourself time to rest. If fatigue persists, worsens or concerns you, seek medical advice.
2. Your sleep feels different
You might spend a full night in bed but wake feeling as though you barely rested, or you may find yourself waking more often than usual or feeling sleepier during the day.
Sleep and immunity are connected, but two different questions matter here: whether sleep affects susceptibility to infection, and whether an infection changes your sleep.
In a study of 164 healthy adults, researchers measured sleep over seven nights before exposing participants to rhinovirus. Those in the shorter-sleep groups - less than 5 hours and 5-6 hours a night - were more likely to develop a clinical cold than those sleeping more than seven hours.3
This study looked at sleep before viral exposure, it does not show a restless night means you are already becoming ill, or that a particular sleep accessory prevents infection.
Changes in sleep can also accompany the immune response to infection. However, a disrupted night on its own cannot tell you whether you’re coming down with something.2
What to consider: Give sleep the best chance it can get. Keep a consistent bedtime, make your bedroom comfortable and allow enough time for a full night’s rest. If you feel run-down, consider reducing your usual demands rather than trying to push through.
Read More: The Four Stages of the Sleep Cycle
3. Your appetite changes
You might find yourself less interested in food than usual or have less enthusiasm for meals you would normally look forward to.
Appetite can change during an infection as the immune system communicates with the brain. Inflammatory signals can influence hunger, motivation and other behaviours as the body coordinates its response.
Researchers refer to some of these changes, which can include fatigue, reduced appetite and social withdrawal, as sickness behaviour.2
A drop in appetite is not a reliable predictor of illness on its own; stress, changes in routine and digestive issues can also affect how hungry you feel. And an unexplained change alongside other symptoms may be worth noticing, but it cannot identify the cause.
What to consider: Keep drinking fluids and eat what feels manageable. If you’re not very hungry, smaller, regular meals may feel easier than a large one. If you cannot keep fluids down, or symptoms are severe or persistent, seek medical advice.
4. You feel unusually hot or cold
You might find yourself reaching for an extra layer, feeling unusually chilly in a warm room or waking up feeling hot and flushed. These changes can sometimes come with shivering or chills.
Feeling hot, cold or shivery can accompany a fever. These are possible symptoms, rather than reliable warnings that appear before an illness begins. Normal body temperature also varies between people and throughout the day.4
What to consider: If you feel feverish, you can check your temperature with a digital thermometer, following its instructions. Consider how you feel overall as well as the reading: feeling hot, cold or shivery may still be relevant even if the thermometer reads below 38°C. Rest, drink fluids and seek medical advice if a fever is worsening or not improving with home care.4
5. Your usual workout feels harder
Your regular workout might suddenly feel more demanding. You may struggle to maintain your usual pace, feel unusually sluggish or find that you need longer to recover from exercise that normally feels manageable.
Wearable research has identified changes in heart rate, sleep and activity around infection, sometimes before reported symptoms. However, those findings do not establish that a workout feeling harder is a reliable predictor of illness.1
A demanding training block, stress or a poor night’s sleep can also make your usual session feel more difficult.
The useful observation is that something feels different from your normal baseline - not that the change confirms you have an infection.
What to consider: Rather than pushing through an unexpectedly difficult session, consider taking a break, especially if you also feel unwell. Prioritise sleep, hydration and adequate nutrition, and if you feel feverish or significantly unwell, pause strenuous exercise and seek professional advice if you’re unsure when to return.
Read More: The Science of Feeling Good: What Your Mind, Body, Skin and Rhythm Need to Thrive
6. A tickly throat, sneezing or a runny nose
A slight tickle in your throat, more sneezing than usual or a runny nose can be easy to dismiss, particularly if you otherwise feel fine. You might notice yourself clearing your throat more often or developing a mild cough that was not there the day before.
These are symptoms in their own right, not signals that appear before all symptoms begin. A sore throat, runny or blocked nose, sneezing and coughing are recognised symptoms of the common cold.5
Of course, not every sniffle means you have an infection; allergies, dry air and other environmental irritants can cause similar symptoms, so consider the bigger picture and how you feel overall.
What to consider: Pay attention to how your symptoms develop. Rest if you’re feeling unwell, stay hydrated and wash your hands regularly. If you have a high temperature or do not feel well enough for your normal activities, stay home and avoid contact with others until you feel better. Seek medical advice if symptoms worsen or are not improving.5
Noticing changes in your energy, sleep, appetite or usual activity can help you recognise when you feel different from your normal baseline. But no single change, and no combination of these six signs, can confirm that you are developing an infection. Give yourself room to rest when you feel unwell, watch how symptoms develop and seek professional advice when symptoms are persistent, worsening or concerning.
3 tools for your everyday rest and relaxation routine
Separate from recognising illness, making time for an everyday wind-down routine can help you create a space for rest and relaxation. You don’t need specialist equipment, but accessories can complement your personal setup.
(Photo of BON CHARGE's Blue Light Blocking Glasses)
1. Blue Light Blocking Glasses: support your wind-down for sleep
A pair of BON CHARGE Blue Light Blocking Glasses can be part of your usual evening routine while you use screens or spend time under artificial lighting. They filter blue and green light to help support your natural circadian rhythm and wind-down routine for better sleep. Always follow the product instructions, including warnings and suitability guidance
2. Blue Light Blocking Lamp: set the evening atmosphere
A BON CHARGE blue-light-free lamp can be part of your evening lighting setup while you read, journal or take time away from screens. Think of it as an accessory for your usual wind-down routine.
3. Blackout Contoured Sleep Mask: block unwanted light
If unwanted light makes your bedroom difficult to darken, a BON CHARGE blackout mask is designed to block light as part of your bedtime routine.
These tools are intended for everyday wellness routines. They are not intended to prevent infection, relieve infection symptoms or speed recovery from illness.
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References
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Mishra, T. et al. Pre-symptomatic detection of COVID-19 from smartwatch data. Nat. Biomed. Eng. 4, 1208–1220 (2020).
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Dantzer, R., O’Connor, J. C., Freund, G. G., Johnson, R. W. & Kelley, K. W. From inflammation to sickness and depression: when the immune system subjugates the brain. Nat. Rev. Neurosci. 9, 46–56 (2008).
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Prather, A. A., Janicki-Deverts, D., Hall, M. H. & Cohen, S. Behaviorally assessed sleep and susceptibility to the common cold. Sleep 38, 1353–1359 (2015).
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National Health Service. High temperature (fever) in adults. NHS (accessed 9 October 2026).
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National Health Service. Common cold. NHS (accessed 9 October 2026).
BON CHARGE: This content is for general education and is not medical advice. Our products are not intended to diagnose, treat, cure, or prevent any disease. Always follow product instructions and consult a qualified healthcare professional for guidance tailored to you. Individual results may vary.
