Palpitations are the feeling that your heart is racing, pounding, fluttering, or skipping — as if it has forgotten its usual quiet job. You might get them after coffee, a fright, too little sleep, or hard exercise, and they often pass. Though actually, they can also be a sign that the heart’s rhythm is not quite right, so doctors take the word seriously even when the cause turns out to be harmless. English nearly always uses the plural: people say they have palpitations, not that they have “a palpitation,” though a doctor may talk about an episode. This is the word patients bring into the clinic. It sounds medical, but it is also ordinary: anyone who has felt their heart jump in bed at night already knows the thing, if not the name.