Morning wood.

The medical term for it is nocturnal penile tumescence, and there's some pretty interesting science behind it.

It has everything to do with our sleep cycle...

...which is why you may have noticed it can happen several times throughout the night.

Sleep happens in stages, stepping us gradually down into deep sleep, which is followed by a spike into shallower rapid eye movement (REM) sleep — the dream stage.

During REM, our brains slow the release of chemicals called neurotransmitters.

It's how the brain regulates our automatic body functions. It also keeps us from doing stuff like unconsciously attempting to act out our dreams.

One of those neurotransmitters — norepinephrine — plays a role in restricting blood flow.

During REM, norepinephrine becomes less active, which opens up blood vessels and increases circulation throughout our body — including to the penis.

The extra blood flow means more oxygen for all parts of our bodies, which is important for standard maintenance and repair.

Erections occur in the mornings because we often wake up just out of REM.

Full bladders may also cause morning wood.

The increased size of the bladder can stimulate a part of the spinal cord that causes a reflex erection to prevent urination during sleep.

So no need to be confused...

or freaked out...

or angry about it.

Because it's just our physiology.

Watch the full explainer below:

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