Palpitation is an awareness of the abnormal beating of the heart. It may occur in people with or without heart problems. Heart palpitations when lying down is not a common occurrence and can be caused by various factors.
Flat feet occur when the normal foot arches have partially or completely collapsed. When the foot is put to the ground the inner or middle side of the foot comes down to the floor rather than remaining raised. This can cause the whole foot to roll inwards (this is called over-pronation).
Overpronation of the foot is not an injury itself but if you over pronate then you may be more susceptible to a number of sports injuries. It is often recognised as a flattening or rolling in of the foot but it is not quite as simple as that as the timing of when the foot rolls in is also important.