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 or go to an emergency department if you have possible signs of sepsis, including:
New confusion, unusual drowsiness, or difficulty staying awake
Fainting, severe dizziness, or cold and clammy skin
Trouble breathing or very rapid breathing
Very little urine
Severe weakness or a rapid worsening of your condition
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 same-day medical assessment if you have fever with persistent pain in your side or back, especially if you also have a urinary infection, kidney stone, diabetes, a weakened immune system, or a recent urinary procedure.
You also need urgent review if symptoms from a diagnosed kidney infection are worsening or have not begun to improve after several days of prescribed treatment.
Do not stop or change antibiotics without medical advice.
After treatment, contact your healthcare team promptly if fever or worsening pain returns, a drainage tube stops working or comes out, or the area around the tube becomes increasingly red, swollen, or painful.
Every sign above is quoted from the sofidex article on Perirenal abscess. If you are not sure, err upward — it is always reasonable to be checked.