it is very common to sense your heart beat while lying in bed -- rarely is it anything serious but certainly this sensation will be aggravated if your blood pressure is high. if your blood pressure is normal it most likely is not a cause of concern. it may also be intensified by any heightened "catecholamine" release (for example adrenaline) state such as caffeine consumption anxiety fear etc.
when lie down i hear my heart beating very loudly in my ears. i have borderline high blood pressure could that be it?