Men, when you wake up to that surprise in your lower region, you no longer need to feel embarrassed. In fact, 'morning wood' is a way of your body telling you that everything is in order, and working fine and dandy.
The reason for 'morning wood' or rather the nocturnal penile tumescence (NPT) as it is known among medical professionals, doesn't have to do with any dirty dreams you may have been having that night. In fact, infant boys inside of the womb also experience NPT. The reason for NPT is the release of a chemical called Nitric Oxide in the nerves of your Johnson during REM sleep - the deep sleep that allows you to dream.
The chemical Nitric Oxide is only released subconsciously by the body during REM sleep in order to make sure everything is in order. However, if you are sleep deprived and not experiencing this process and your body isn't checking to see if your man clock is still ticking. Thus, sleep deprivation actually lead to erectile dysfunction.
Men, get your sleep. For more information on morning wood - read the source!