There are 3 types of erections, according to medical doctors, with this reference coming from Dr. Marais from Busamed Private Hospital in Somerset West.Post your references here, please
First is psychogenic, or the sexual one. Second is the reflexive, caused by touch or irritation of the nerves. Third is nocturnal which occur during sleep, and the expectation of physiology is 5 or more throughout the night is healthy.
Other research I have done includes surges in testosterone in the morning can cause morning erection.
tl: dr-Not all erections are sexual.