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 for sudden arm weakness when it could be a stroke, especially if there is also:
Facial drooping
Trouble speaking or understanding speech
New weakness or numbness on one side of the body
Sudden loss of balance, vision or coordination
A sudden, severe headache
Emergency care is also appropriate after a major arm injury if the hand is cold, pale or blue; there is severe bleeding; a bone or deep tissue is exposed; or pain and swelling are rapidly worsening.
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 medical assessment for new wrist or finger weakness, particularly after an injury.
You should also get prompt help if a cast or bandage is followed by increasing pain, numbness, swelling, colour change or difficulty moving the fingers.
3
Does any of this apply?
Book an appointment
Arrange a routine appointment for persistent tingling, numbness or pain on the back of the hand, or for weakness that is mild but not improving.
Follow-up is also important if known radial nerve dysfunction worsens or recovery stops progressing.
Every sign above is quoted from the sofidex article on Radial nerve dysfunction. If you are not sure, err upward — it is always reasonable to be checked.