Spontaneous Orgasm

How and more importantly why do men sometimes ejaculate without having an erection?

Further information was provided after I asked some more questions, specifically:

Without erection at all, arousal being anything from nothing to an unusually stunning person. Right before, my testicles get very ticklish and there's a euphoric tingling sensation. This usually happens while sitting down.

This question took me a really long time to get around to answering. The reason for this is because I'd actually never heard of this before and when I talked to the medical professionals that I know (and also someone at Planned Parenthood) they were all pretty puzzled. In researching I have found some information that may help you though.

An erection is not required to have an orgasm or to ejaculate. While they are all often tied together in our minds because they all usually happen together, there are different things going on in each and none are required to make the other one happen. However, this is mostly talked about with men who cannot get an erection.

When it comes to spontaneous orgasm it looks like the most likely culprit is antidepressants. There have been studies done that show that spontaneous orgasm is actually a side effect to antidepressants including: Wellbutrin, Paxil, Prozac, and Celexa. Most of the studies have been done on women and some report having as many as 15 spontaneous orgasms per day with very little or no stimulation whatsoever. So if you're on an antidepressant that may be what is causing it. Either way though you should probably go to a doctor and get yourself checked out. Spontaneous orgasms, especially ones where you ejaculate, can become pretty embarrassing in public situations.