Our hearts have to beat harder and faster when under stress or when doing some physical activities.
The palpitation which you should seek medical help occurs when your heart suddenly beats at 130/min or more when you are at rest and not stressed. Or when you feel irregular heart beat. This is when you feel your pulse, it feels totally chaotic without any regular rhythm.
You should also see your doctor if there is chest pain or breathlessness accompanying your palpitation. On the other hand, the occasional ‘dropped beat’ is usually benign. As long as they do not bother you and do not cause any other symptoms, it is usually harmless.