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 a sudden taste change occurs with signs that could indicate a stroke, such as:
Facial drooping
Weakness or numbness on one side
Trouble speaking or understanding speech
Sudden severe dizziness, loss of balance, or vision change
Breathing difficulty is 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
Seek same-day medical advice if the change follows a significant head injury, or if swelling of the tongue or throat makes it difficult to breathe or swallow.
And for anyone, someone who:
has a wound that is hot, spreading red, or leaking pus
3
Does any of this apply?
Book an appointment
Arrange a routine appointment if impaired taste lasts several weeks, keeps worsening, repeatedly returns, or has no clear explanation.
You should also book an appointment if it is causing weight loss, poor nutrition, difficulty eating, persistent mouth sores, dental pain, or severe dry mouth.
The article also says
A taste change that begins after starting a medicine should be discussed with a doctor or pharmacist.
Do not stop a prescribed medicine on your own unless you are advised to do so.
Every sign above is quoted from the sofidex article on Taste - impaired. If you are not sure, err upward — it is always reasonable to be checked.