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 someone with possible severe hypothyroidism has marked confusion, cannot stay awake, loses consciousness, has very slow or difficult breathing, or is unusually cold and seriously unwell.
Chest pain or severe breathing difficulty also requires emergency assessment, whatever the suspected cause.
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 for a rapidly enlarging neck swelling, new trouble swallowing, or a persistent unexplained voice change.
3
Does any of this apply?
Book an appointment
Arrange a routine appointment if you have persistent symptoms such as tiredness, cold intolerance, constipation, unexplained weight change, heavy periods, or swelling at the front of your neck.
These symptoms have many possible causes, so testing is important.
Also arrange follow-up if:
Symptoms return or continue after treatment
You develop symptoms that could suggest too much replacement hormone
You start or stop medicines or supplements that may affect levothyroxine
You have difficulty taking your medicine consistently
You are planning a pregnancy or have a positive pregnancy test
Every sign above is quoted from the sofidex article on Hypothyroidism. If you are not sure, err upward — it is always reasonable to be checked.