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 possible epiglottitis.
Warning signs include:
Difficulty breathing or rapidly worsening breathlessness
Stridor or another unusual noise when breathing in
Drooling or inability to swallow saliva
Blue, grey, or unusually pale lips or skin
Sitting forward or refusing to lie down to breathe
Severe throat pain with a muffled voice or breathing change
Sudden worsening after a throat burn or chemical exposure
Do not drive someone with breathing difficulty to hospital if emergency transport is available.
An ambulance team can provide oxygen and airway support if the condition worsens on the way.
Call emergency services again if any breathing difficulty, stridor, or drooling returns.
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
After hospital treatment, contact the treating service promptly for returning fever, increasing throat pain, renewed difficulty swallowing, or inability to take prescribed medicine.
The article also says
Keep the person upright and as calm as possible while waiting for help.
Do not force them to lie down.
Do not examine the throat, place anything in the mouth, or give food, drink, or oral medicine if swallowing or breathing is difficult.
Every sign above is quoted from the sofidex article on Epiglottitis. If you are not sure, err upward — it is always reasonable to be checked.