One of the most common health dilemmas is deciding whether a symptom warrants a visit to the doctor or whether it will resolve on its own. Getting this judgement right matters — going too late can allow treatable conditions to progress, while going unnecessarily puts pressure on healthcare systems and your wallet.
Here are ten warning signs that should prompt you to seek medical attention promptly, along with guidance on how urgently to act.
1. Chest pain or pressure
Any new chest pain, pressure, tightness, or heaviness should be taken seriously. While not all chest pain is a heart attack — it can also be caused by muscle strain, acid reflux, or anxiety — you should seek emergency care immediately if chest pain is severe, spreading to your arm or jaw, accompanied by shortness of breath or sweating, or if you have known heart disease risk factors.
Action: Call 999/112 immediately for any severe, unexplained chest pain.
2. Sudden severe headache
A headache described as "the worst of my life" or one that comes on suddenly and severely — sometimes called a thunderclap headache — can indicate a brain aneurysm or subarachnoid haemorrhage. This is a medical emergency. Most headaches are not dangerous, but this pattern is a red flag.
Action: Call 999/112 immediately for a sudden, severe "thunderclap" headache.
3. Difficulty breathing
Shortness of breath that is new, unexplained, or significantly worse than usual should be assessed urgently. It can indicate heart failure, pulmonary embolism (blood clot in the lung), severe asthma, pneumonia, or anaphylaxis. If breathing difficulty comes on suddenly or severely limits your ability to speak or move, call for emergency help immediately.
4. High or persistent fever
A fever above 39.5°C (103°F) in adults, or any fever in infants under three months, warrants prompt medical attention. A fever that persists for more than three days, is accompanied by severe headache and stiff neck, causes confusion, or does not respond to paracetamol or ibuprofen should be assessed by a doctor the same day.
5. Unexplained weight loss
Losing more than 5% of your body weight over six to twelve months without trying can be a sign of underlying illness — including diabetes, thyroid disease, depression, coeliac disease, or in some cases cancer. This symptom should never be dismissed, particularly in people over 50.
Action: Book a non-urgent GP appointment within two weeks.
6. Blood where there should not be any
Blood in urine, stool, vomit, or sputum always warrants medical assessment, even if the amount is small. Causes range from easily treatable conditions to serious ones requiring urgent investigation. Do not assume it is haemorrhoids, and do not wait to see if it resolves.
7. New or changing moles
The ABCDE rule helps identify concerning skin changes: Asymmetry, irregular Border, multiple Colours, Diameter larger than 6mm, and Evolution or change over time. Any mole that itches, bleeds, or changes in size, shape, or colour should be assessed by a GP, who may refer you to a dermatologist.
8. Sudden weakness or numbness on one side
Sudden weakness, numbness, or paralysis on one side of the body — particularly affecting the face, arm, or leg — along with speech difficulties or sudden vision problems, are classic symptoms of stroke. Remember the FAST test: Face drooping, Arm weakness, Speech problems, Time to call 999/112.
Action: Call 999/112 immediately. Time is critical — every minute counts in stroke treatment.
9. Severe or persistent abdominal pain
While stomach aches are common and usually harmless, severe abdominal pain — particularly if it is constant, worsening, or accompanied by fever, vomiting, or inability to pass wind — should be assessed urgently. Causes requiring prompt treatment include appendicitis, bowel obstruction, and ectopic pregnancy.
10. Mental health concerns
Any thoughts of self-harm or suicide, or a significant deterioration in mental health, should prompt contact with a healthcare professional the same day. Mental health emergencies are as real as physical ones. If someone is in immediate danger, call emergency services or go to your nearest A&E department.
When in doubt, check your symptoms first
Not sure whether your symptoms warrant a call to your GP? Our free AI-powered symptom checker can help you understand what your symptoms might mean and how urgently you should act — in under 60 seconds, with no account required.
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A note on emergency numbers
If you are unsure which number to call in your country, our emergency numbers directory covers ambulance, police, and crisis lines for over 50 countries worldwide.
Editorial note: This article was written by the SymptomSense editorial team in accordance with our editorial policy. It is reviewed against NHS, WHO, and Mayo Clinic guidelines and updated regularly. Last reviewed June 2026. This article is for informational purposes only and does not constitute medical advice.