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 if neck swelling is making it hard to breathe.
Get emergency help as well if you cannot swallow saliva, are drooling because swallowing is difficult, or the swelling is increasing rapidly and affecting your airway.
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 same-day medical advice if a swollen area is red, hot, very painful, or rapidly enlarging, especially with a fever.
These changes may indicate an infection that needs prompt treatment.
You should also seek prompt advice if you feel very unwell or have a weakened immune system.
And for anyone, someone who:
has a wound that is hot, spreading red, or leaking pus
3
Does any of this apply?
Book an appointment
Book a routine appointment if the swelling:
Lasts for several weeks, keeps growing, or has no clear cause
Feels hard, irregular, or fixed in place
Is above or below the collarbone
Appears in several unrelated areas
Occurs with ongoing fever, drenching night sweats, or unexplained weight loss
These features do not identify a particular condition.
They mean that checking the cause is important.
And for anyone, someone who:
has noticed a lump, a mole that has changed, or unexplained weight loss
Every sign above is quoted from the sofidex article on Swollen lymph nodes. If you are not sure, err upward — it is always reasonable to be checked.