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 the movement begins suddenly with:
Face drooping, one-sided weakness, or difficulty speaking
Loss of awareness, severe confusion, or trouble waking
A seizure lasting more than five minutes
Repeated seizures without recovery between them
Trouble breathing, blue or grey lips, or a serious injury
A severe headache, especially with weakness or confusion
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 for a new movement with fever, marked stiffness, severe agitation, or a recent medicine or dose change.
Prompt advice is also important if the movement began after a head injury or possible exposure to a poison or recreational drug.
3
Does any of this apply?
Book an appointment
Book a routine appointment if the movement keeps returning, is getting worse, affects sleep or daily activities, or causes pain, falls, embarrassment, or injury.
New persistent movements also deserve assessment, even when they are mild.
The article also says
During a seizure, protect the person from nearby hazards, cushion their head, and turn them onto their side when possible.
Do not restrain them or place anything in their mouth.
Every sign above is quoted from the sofidex article on Movement - uncontrollable. If you are not sure, err upward — it is always reasonable to be checked.