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
Get emergency help for trouble breathing, blue or grey lips, a seizure, loss of consciousness, severe confusion, new weakness, or difficulty waking.
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
Arrange routine or same-day medical advice if:
Drinking is difficult because of mouth pain
Wet diapers or urination are noticeably less frequent
Fever lasts more than three days
Symptoms are severe or are not improving after about 10 days
Blisters develop increasing redness, swelling, pain, or pus
The person has a weakened immune system
A very young baby develops symptoms
Seek urgent medical help if there are signs of significant dehydration, such as very little or no urine, marked drowsiness, a very dry mouth, sunken eyes, or an inability to keep fluids down.
A severe headache with a stiff neck, repeated vomiting, sensitivity to light, unusual sleepiness, or rapidly worsening illness also needs urgent assessment.
These symptoms can have several causes and do not automatically mean there is a serious complication, but they should not be managed at home without advice.
Every sign above is quoted from the sofidex article on Hand-foot-mouth disease. If you are not sure, err upward — it is always reasonable to be checked.