Why are some dreams so real?

Q: What actually causes the heart to beat? Sometimes, some dreams are so real that we have a real feeling of falling down. Though its all only in the mind, how does that shock cause us to fall down from our bed?

A:The heart is composed of contractile muscle. Within the heart there is a pacemaker that sends out electrical impulses, via nerves, to all parts of the heart. Each time the pacemaker sends a pulse of electricity out through its network of nerves, the heart muscle contracts, forcing blood throughout the body.Dreams are of various sorts, and some people have very vivid dreams. In such cases, the dreaming brain instructs the body to move or jerk, and this may cause the person to fall off the bed.