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
Seek emergency help if palpitations or irregular beats occur with:
Chest pain or pressure
Fainting or near-fainting
Severe or rapidly worsening breathlessness
New one-sided weakness, facial drooping, or difficulty speaking
A sustained very fast heartbeat with marked dizziness or collapse
Do not drive yourself for emergency care if you feel faint or severely unwell.
And for anyone, someone who:
has chest pain, tightness or pressure lasting more than a few minutes
Other emergency signs, for anyone
Someone who is struggling to breathe, gasping, choking, or cannot get words out
Someone who has sudden weakness or drooping on one side of the face or body, slurred speech, or sudden confusion
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
Prompt assessment is especially important if you have fainted during exercise or have a family history of unexplained sudden death at a young age or inherited heart rhythm disease.
Urgent medical advice may still be needed if these symptoms have stopped.
And for anyone, someone who:
is getting rapidly more short of breath, or has gained several pounds in a few days with swelling
3
Does any of this apply?
Book an appointment
Arrange a routine appointment if the sensations are new, keep returning, become more frequent, last longer than before, or interfere with sleep or activity.
Seek assessment if you have known heart disease.
A routine assessment can identify the rhythm if symptoms continue to worry you.
The article also says
An isolated thump or skipped sensation without concerning symptoms is not usually an emergency.
Every sign above is quoted from the sofidex article on Ectopic heartbeat. If you are not sure, err upward — it is always reasonable to be checked.