Dr Rob Hicks replies: If you don't already have heart problems then your symptoms are unlikely to be serious, but you should see your doctor to get checked out. Many people experience similar symptoms to yours and are found to have no underlying problem. In fact, once they learn this their symptoms invariably disappear.
Caffeine, alcohol, nicotine and some recreational drugs can cause the heart to beat faster so avoid these, particularly before going to bed. Other common causes are stress or anxiety so these should be kept under control with relaxation techniques. At night many people become more aware of their body so what is often a normal heartbeat becomes more obvious.
It's a good idea to have your blood pressure checked regularly. Not smoking, exercising regularly and keeping your weight in check will help to keep your heart healthy.