According to your symptoms (palpitations during sleep or after drinking energy drinks), you might be experiencing some type of sudden tachycardia. Tachycardia can be diagnosed only with an apparatus that conducts a 24 hours monitor of the heart rhythm; it is called a holter. Energy drinks contain a lot of caffeine. Caffeine may cause such episodes of tachycardia. Anxiety in young people can also cause the feeling that the “heart beats heavily”, even if there is no tachycardia present. You may visit your primary health doctor if these palpitations become more frequent and request the 24 hour monitor.