Go through these in order and stop at the first one that applies. If you are reading this for someone else, answer for them.
Follow your emergency steroid plan if you have one.
Call emergency services for possible adrenal crisis, especially with:
Use an emergency steroid injection as instructed, but do not delay emergency care.
Seek urgent medical advice if you take cortisol replacement and develop vomiting or diarrhoea that prevents you from keeping medicine down.
Arrange routine medical review if you have a history of severe childbirth bleeding and later develop persistent fatigue, low blood pressure, absent periods, difficulty producing breast milk, reduced body hair, or unexplained low sodium or low blood sugar.
These symptoms have several possible causes and need proper assessment rather than self-diagnosis.
Routine blood tests and treatment reviews should continue even when you feel well.
The article also says
If you have diagnosed Sheehan syndrome, contact your usual care team when symptoms change, medicines are repeatedly missed, or you are planning pregnancy, surgery, or prolonged travel.
Every sign above is quoted from the sofidex article on Sheehan syndrome. If you are not sure, err upward — it is always reasonable to be checked.