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
Seek emergency medical help for anyone with fever or recent illness who develops:
Confusion, unusual behaviour, or difficulty waking
A seizure, especially a first seizure
Sudden weakness, paralysis, or loss of coordination
A severe headache with a stiff neck
Problems breathing or swallowing
Loss of consciousness
This is preventive planning rather than an emergency.
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
Do not wait for a rash or for every typical symptom to appear.
Encephalitis can have several causes, and early hospital assessment is important.
3
Does any of this apply?
Book an appointment
Arrange routine medical follow-up after discharge if memory, mood, movement, speech, swallowing, seizures, or daily functioning are not improving as expected.
Routine review is also appropriate when symptoms interfere with school, work, sleep, or personal care.
The article also says
If you are planning travel to an area where Japanese encephalitis occurs, seek travel health advice before departure.
Every sign above is quoted from the sofidex article on Russian autumnal encephalitis. If you are not sure, err upward — it is always reasonable to be checked.