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 for:
Difficulty breathing, noisy breathing, or blue or grey lips
Drooling or inability to swallow
Rapidly increasing neck swelling
Chest pain, fainting, or a fast or irregular heartbeat
Sudden severe weakness, paralysis, or difficulty staying awake
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 assessment now if you or someone in your care has a thick grey or white throat coating, marked neck swelling, or possible diphtheria symptoms after a known exposure or recent stay in an affected area.
Call ahead before arriving so infection-control precautions can be arranged.
Contact a healthcare or public health service promptly if you have been identified as a close contact, even if you feel well.
Preventive treatment works best when arranged without delay.
New chest, breathing, swallowing, or weakness symptoms during recovery need prompt assessment.
3
Does any of this apply?
Book an appointment
Follow-up may include vaccine review, repeat cultures, heart or nerve checks, and planning a gradual return to activity.
The article also says
Do not try to remove a throat membrane.
Every sign above is quoted from the sofidex article on Diphtheria. If you are not sure, err upward — it is always reasonable to be checked.