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 you have signs of severe illness, such as confusion, fainting, difficulty breathing, mottled skin, or extreme weakness.
These symptoms are uncommon with a pilonidal sinus but can indicate a serious response to infection.
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 prompt medical care if you develop:
A rapidly growing or very painful swelling
Pus draining from a new lump
Fever or chills
Redness spreading away from the cleft
Increasing pain after a procedure
Heavy bleeding or a surgical wound that opens
3
Does any of this apply?
Book an appointment
Arrange a routine appointment if you notice a new pit, repeated tenderness, or ongoing drainage in the buttock cleft.
It is also reasonable to seek review if symptoms interfere with sitting, exercise, work, or sleep, even when the pain is not severe.
The article also says
People with a weakened immune system or poorly controlled diabetes may need earlier assessment because infections can become more difficult to manage.
Every sign above is quoted from the sofidex article on Pilonidal sinus disease. If you are not sure, err upward — it is always reasonable to be checked.