The most important sex organ in between the ears, not between the hips. It is possible to produce an orgasm in oneself with nothing more than “mental masturbation.” My earliest orgasms were produced in this way (good Catholic girls didn’t even KNOW about female masturbation back then!). Wish I could still do it! 
Anyway if you have ever had a sexual dream and been woke up by the orgasm, that’s pretty much what’s happening.
Of course mental sex is possible. Haven’t you people ever heard the term mind fuck?
Oh, oh, wet dreams, yes, I was going to bring that up (no pun)…
But then thats more like unconscious mental masturbation isn’t it?
I think, If you get Waaayyy farther into than I ever delved, Tantric philosophy gets into stuff like that.
I think if you can enter people’s minds like that you won’t need sex, as sex would be tiny by comparsion.