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
These symptoms need assessment but are not always an emergency.
Call emergency services for:
Severe difficulty breathing at rest
Chest pain or pressure
Fainting, confusion, or difficulty waking
Blue or grey lips
Signs of shock, such as cold clammy skin with marked weakness
Severe symptoms beginning during a blood transfusion
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
Arrange routine or prompt follow-up if you develop increasing tiredness, mild breathlessness, yellowing of the eyes, dark urine, or reduced ability to manage normal activities.
Seek urgent same-day medical care for rapidly worsening jaundice, new dark or red urine with weakness, a very fast heartbeat, fever during immune-suppressing treatment, or symptoms following a blood transfusion.
If you do not have a functioning spleen, fever or feeling suddenly very unwell needs urgent assessment because serious infections can progress quickly.
The article also says
Do not drive yourself if you feel faint, confused, or severely short of breath.
Every sign above is quoted from the sofidex article on Hemolytic anemia. If you are not sure, err upward — it is always reasonable to be checked.