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 symptoms that may indicate a pulmonary embolism, including:
Stroke symptoms are also an emergency.
These include sudden facial drooping, arm weakness, speech difficulty, loss of vision, or a severe new neurological problem.
If you take an anticoagulant, emergency assessment is needed for uncontrolled bleeding, vomiting blood, black stools, a major injury, or a significant blow to the head.
Sudden severe headache, weakness, or confusion also needs emergency care.
Seek urgent same-day medical assessment for new swelling, pain, warmth, or colour change in one leg, particularly when symptoms appear after surgery, travel, illness, or reduced mobility.
Arrange routine follow-up to discuss pregnancy plans, contraception containing oestrogen, an upcoming operation, persistent symptoms after a clot, or concerns about anticoagulant side effects.
These situations need planning but are not usually emergencies when you otherwise feel well.
Every sign above is quoted from the sofidex article on Congenital antithrombin III deficiency. If you are not sure, err upward — it is always reasonable to be checked.