Definitions by Dr.Pascalle

morning wood 

A morning erection that is naturally caused as the brains enters the REM-deep sleep phase. At this stage, the body's skeletal muscle structure relaxes and causes hypervasodilation in the capillaries of the body, resulting in said erection.

After sleeping so soundly and having a great night's rest, it is no surprise to wake up with an erection.

morning wood by Dr.Pascalle December 2, 2004