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The seriousness depends on the origin and nature of the beats / underlying cause / associated morbidities and so on.
There are several causes - Anxiety / Alcohol / Tobacco (smoking) / Caffeine (too much coffee, cola) / Medicines like Phenylephrine
used for ‘cold’; Salbutamol
used for asthma / Illicit ‘drugs’ like Amphetamine
/ anaemia / thyroid / heart disease
including abnormal nerve paths (bypass tracts) - the list is long...
You must go the ER / see a doctor / get examined / get investigated.
Wishing speedy recovery