In most cases palpitations are not dangerous, but a number of combinations of symptoms considerably increase the likelihood of a serious cardiac cause. The evidence for this comes from observational and diagnostic research of moderate quality. In practical terms this means: if you faint, experience symptoms during exertion, have recently started new medication, or are young and regularly experience palpitations, a visit to the doctor is necessary and not an excessive precaution.
Palpitations are a common complaint in general practice and in most cases have a harmless cause. Even so, they can sometimes be the first sign of a serious cardiac arrhythmia or structural heart disease. With a thorough medical history, physical examination and an ECG, a doctor can in most cases distinguish between something innocent and something that warrants further attention.
There are a number of situations in which you should not wait but call a doctor immediately or go to the emergency department. Palpitations accompanied by fainting or loss of consciousness are a serious warning sign: research in young people shows that palpitations occurring before a person faints more than double the likelihood of a serious cardiac cause (odds ratio 2.6). Palpitations that occur during or immediately after physical exertion, and palpitations accompanied by dizziness, chest pain or shortness of breath, also call for prompt medical assessment.
Extra vigilance is warranted specifically for young people. A screening study among 1,472 young individuals found that 23.5% reported having experienced palpitations at some point. Because palpitations in young people can be a warning signal for serious heart disease and even sudden cardiac death, it is recommended that, in addition to a questionnaire, an ECG be obtained for a proper risk assessment.
Have you recently started new medication and are you now experiencing palpitations, dizziness or near-fainting? Consult your doctor or pharmacist. Some medicines can disrupt the heart rhythm through a mechanism called 'QT prolongation', which in rare cases can lead to a dangerous arrhythmia called 'torsades de pointes' and, in extreme cases, to ventricular fibrillation and sudden cardiac death.
Palpitations can also indicate low blood sugar (hypoglycaemia), even in people without diabetes. Other early signs include blurred vision, dizziness, trembling, sweating and nausea. If left untreated, loss of consciousness may follow. When this combination of symptoms is recognised, rapid action is required. Finally, it is worth knowing that diagnosing palpitations requires specialist expertise: a Mayo Clinic study showed that 41% of patients referred with a diagnosis of 'long QT syndrome' (an inherited cardiac arrhythmia) turned out not to have the syndrome at all. Self-diagnosis based on an app or a single ECG recording is therefore inadvisable.
The claims are based on multiple published studies (PMID 32888682, 34379354, 21066971, 31990841, 21894674, 17502575, 20634114, 15647542). These are observational and diagnostic studies of moderate quality of evidence; no large randomised trials exist on this diagnostic topic, which is not expected for this type of question. The claims relating to narcolepsy and environmental odours are insufficiently supported and have not been included in the answer as a clinical action point.