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 for sudden dizziness or vertigo with:
Face drooping, one-sided weakness or numbness, or trouble speaking
New double vision, confusion, or inability to stand or walk
A sudden severe headache or severe new neck pain
Chest pain, marked shortness of breath, or fainting
Symptoms following a significant head injury
Do not drive yourself if you may be having a medical emergency.
And for anyone, someone who:
has sudden weakness or drooping on one side of the face or body, slurred speech, or sudden confusion
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 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 same-day medical care for new hearing loss in one ear, repeated vomiting that prevents you keeping fluids down, a rapid or irregular heartbeat, or new persistent dizziness that makes walking unsafe.
3
Does any of this apply?
Book an appointment
Book a routine appointment if dizziness keeps returning, lasts longer than expected, causes falls, or disrupts daily life.
Arrange follow-up if it began after starting or changing medicine, or occurs with ongoing headaches, ringing in the ears, or gradual hearing changes.
Every sign above is quoted from the sofidex article on Dizziness and vertigo. If you are not sure, err upward — it is always reasonable to be checked.