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 if very high blood pressure occurs with chest pain, severe breathlessness, new weakness or numbness, confusion, trouble speaking, major vision changes, seizure, fainting, or a sudden severe headache.
Do not drive yourself.
Contact your healthcare service promptly if a reading is above 180/120 mm Hg.
Sit quietly, make sure the cuff is positioned correctly, and repeat the measurement after at least one minute.
If it remains that high but you have no concerning symptoms, seek same-day professional advice rather than changing medicine yourself.
During pregnancy or soon after giving birth, seek urgent medical advice for high readings, severe headache, vision changes, pain under the ribs, vomiting, sudden swelling, or difficulty breathing.
These symptoms can occur with pre-eclampsia and need prompt assessment.
Arrange a routine appointment if several properly taken readings are above the normal range, even if you feel well.
Also seek routine advice if your readings are becoming higher over time, you are having medication side effects, or you are struggling to take treatment consistently.
Every sign above is quoted from the sofidex article on Hypertension. If you are not sure, err upward — it is always reasonable to be checked.