I smoked some salvia and had an involuntary orgasm and ejaculation. My mind was focused on sex before I smoked.
Salvia always seems to induce time-lag in perception; I think that's part of the reason why Salvia creates the hallucinations it does. You're receiving visual information that's not propagating along normal channels at normal speeds, which seriously changes your perception of the surrounding world. Senses beyond the visual are likely affected too. Neural signals all over are definitely affected, even if the most drastic changes seem to happen to the visual field.
What I feel may have happened to you is this;
1. You were focused on sex. Therefore neural signals related to sex were in your mind at that immediate time.
2. You took Salvia, which induces time-compression. Take the metaphor of a variable microscope that can go from normal magnification to 100x. The object gets no bigger, but one's perception of it has it getting dramatically larger. In this case, take your sexual thoughts, which are essentially magnified, dived into, as the time-compression takes a thought that might last milliseconds but now lasts seconds or even a minute. Normally sober those thoughts about sex were the size of streams; slowed down and compressed, in your perception they became a huge river.
3. You splurge.
The process possibly mirrored what happens in a wet dream, however the hell those work. That's just my conjecture from my experience. Thanks for sharing this, weird as it may seem; it doesn't seem an unusual outcome to me given what I know of Salvia.