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 weakness or numbness, especially on one side
Facial drooping, speech difficulty, confusion, or sudden loss of balance
New severe difficulty breathing
Inability to swallow saliva or repeated choking
Rapidly spreading weakness
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 advice if weakness is worsening over days, you are choking during meals, or you have new trouble walking or using a hand.
3
Does any of this apply?
Book an appointment
Arrange a routine medical appointment if you notice unexplained muscle shrinking, continuing weakness, repeated falls, or difficulty with activities that used to be manageable.
Assessment is also important for ongoing weight loss, poor appetite, numbness, muscle twitching, or symptoms affecting only one side.
The article also says
Sudden one-sided weakness and speech or facial changes can be signs of a stroke.
Breathing and swallowing problems may mean that important muscles are not working safely.
Every sign above is quoted from the sofidex article on Muscle atrophy. If you are not sure, err upward — it is always reasonable to be checked.