Go through these in order and stop at the first one that applies. If you are reading this for someone else, answer for them.
Call emergency services for sudden loss of vision, new facial drooping, arm weakness, difficulty speaking, or other possible stroke symptoms.
Do not drive yourself for emergency assessment.
Seek urgent same-day medical help if you have a new headache, scalp tenderness, jaw pain when chewing, or temporary visual disturbance.
These symptoms may indicate GCA and should not wait for a routine appointment.
Arrange a routine medical appointment if you develop persistent pain and morning stiffness in both shoulders or hips, particularly if you are over 50.
Similar symptoms can have several causes, so an assessment is needed rather than self-diagnosis.
The article also says
During treatment, contact your usual healthcare service if symptoms return, become harder to control, or do not improve as expected.
Also report possible steroid side effects such as unusual thirst, frequent urination, repeated infections, major mood changes, or new vision difficulties.
Every sign above is quoted from the sofidex article on Polymyalgia rheumatica. If you are not sure, err upward — it is always reasonable to be checked.