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 now if back pain occurs with:
New inability to urinate or new loss of bladder or bowel control
New numbness around the genitals, inner thighs, or buttocks
Rapidly worsening weakness in one or both legs
Severe chest or abdominal pain, fainting, or difficulty breathing
A major crash, fall, or other high-force injury
And for anyone, someone who:
is bleeding heavily and it will not stop with firm pressure
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 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
Prompt assessment matters.
Seek same-day medical advice if you have fever or chills, feel seriously unwell, or have severe pain after a smaller fall when you have osteoporosis or fragile bones.
Also seek prompt advice if you have a weakened immune system, inject drugs, recently had a serious infection or spinal procedure, or have a history of cancer.
Arrange assessment sooner if leg pain, numbness, or weakness is developing.
And for anyone, someone who:
has abdominal pain that is severe, constant, or getting worse
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 pain is not starting to improve after one to two weeks, keeps returning, limits normal activity, or continues for several weeks.
The article also says
Bladder changes, saddle-area numbness, and leg weakness can indicate serious pressure on spinal nerves.
Every sign above is quoted from the sofidex article on Acute low back pain. If you are not sure, err upward — it is always reasonable to be checked.