There is no controlling a morning erection that I know of except remaining prone and that doesn’t always work if you are fully awake. Get up? Move around? It fades like a lilac blossom.
"It's not the getting there but the going that's gotta be good." Varg
I agree with avocet’s explanation of the nervous system controls, plus Salvo’s comments on the physical environment provided by sleep, but I’m trying to get avocet’s painfully descriptive lilac blossom out of my mind! LOL
I thought the Sympathetic Nervous system only took over in highly stressful situations. When your sympathetic nervous system takes over digestion stops, heart beat accelerates palms sweat, pupils dilate, and bronchial tube expands. Every reaction is designed to increase the amount of oxygen to your brain and muscles to help you fight or flight. I figured the Parasympathetic nervous system is the one at use most throughout our day, as I was under the impression that the sympathetic nervous system can’t take over for long periods of time because of strain on the body and the halt of digestion. I don’t really know thought, just throwing that out in the open.