Why Do Erections and Discharge Hit in Paralyzed Dream Sleep?

On Huberman Lab, involuntary muscles stay unparalyzed during rapid eye movement sleep, which is one reason men have erections and women have vaginal lubrication. The other reason is autonomic activity. Autonomic storms activate the body enough for erections and vaginal discharge, and paralysis continues through them. Only two voluntary muscle groups are spared: the extraocular muscles and the inner ear muscle.

The autonomic nervous system controls automatic behaviors, including aspects of reproductive function. During a storm, heart rate decelerates and drops and blood pressure goes down. Then, utterly at random and with no regular pattern, heart rate accelerates dramatically as the sympathetic nervous system, the fight or flight branch, fires up and shuts down again. The extraocular muscles stay free so rapid eye movements can still happen. The inner ear muscle was later found to be spared as well. There is no good understanding of why the two groups escape paralysis. A cranial nerve explanation is judged unlikely, with a lean toward something more sensory. Some people argue that eyeballs left inactive for long periods may develop oxygen issues in the aqueous or vitreous humor, so the eyeballs have to keep moving.