Why is it called morning wood?

"Morning wood," clinically known as nocturnal penile tumescence, refers to the spontaneous erections that occur in males during sleep or upon waking. This phenomenon is primarily linked to the body's natural sleep cycles, particularly REM sleep, when the body undergoes various physiological changes. The term "morning wood" is colloquial, as these erections are most commonly noticed in the morning. They serve as an indicator of healthy blood flow and erectile function.