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 with any of the following:
Face drooping, arm or leg weakness, numbness, or trouble speaking
New double vision, severe loss of coordination, or inability to walk
Fainting, chest pain, severe breathlessness, or a very irregular heartbeat
A sudden severe headache, confusion, or seizure
Dizziness after a serious head injury
These symptoms can occur with stroke or another emergency.
Do not drive yourself.
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 if dizziness is new and continuous, causes repeated vomiting, or makes it unsafe to stand or walk.
Sudden hearing loss in one ear also needs prompt assessment, particularly with vertigo.
3
Does any of this apply?
Book an appointment
Book a routine appointment if dizziness keeps returning, lasts longer than expected, worsens, or interferes with work, sleep, driving, or daily activities.
Arrange a review if it began after starting or changing a medicine.
Do not stop prescribed medicine without advice.
Every sign above is quoted from the sofidex article on Dizziness. If you are not sure, err upward — it is always reasonable to be checked.