Go through these in order and stop at the first one that applies. If you are reading this for someone else, answer for them.
1
Is any of this happening now?
Call 911
Call emergency services immediately for symptoms that could indicate a stroke, heart attack, clot in the lungs, or major bleeding, including:
Sudden weakness or numbness on one side
A drooping face, new speech difficulty, or sudden confusion
Sudden loss of vision or a severe, unfamiliar headache
Chest pressure, severe chest pain, or sudden breathlessness
Coughing or vomiting blood
Heavy bleeding that does not stop
Collapse, fainting, or severe drowsiness
Other emergency signs, for anyone
Someone who is struggling to breathe, gasping, choking, or cannot get words out
Someone who has chest pain, tightness or pressure lasting more than a few minutes
Someone who has sudden weakness or drooping on one side of the face or body, slurred speech, or sudden confusion
Someone who is unconscious, or cannot be woken
Someone who is bleeding heavily and it will not stop with firm pressure
Someone who has had a seizure that will not stop, or does not wake up afterwards
Someone who has lips or skin that look pale, blue, grey or blotchy
Someone who you believe has taken an overdose or swallowed something poisonous
2
Is any of this happening?
Be seen today
Seek urgent medical advice for new one-sided leg swelling or pain, repeated bleeding, black or bloody stools, blood in the urine, or suddenly worsening headaches or vision problems.
3
Does any of this apply?
Book an appointment
Keep follow-up appointments even when you feel well.
The article also says
Contact your haematology or primary care team if symptoms gradually change, side effects are difficult to manage, or you have questions about pregnancy, travel, surgery, dental work, or new medicines.
Every sign above is quoted from the sofidex article on Essential thrombocythemia. If you are not sure, err upward — it is always reasonable to be checked.