Don't feel silly. You are far from the only person to worry about having some terrible condition misdiagnosed as CPPS.
I'm not a doctor, so don't take this as diagnosis, but I very much doubt you have Stiff-Person Syndrome. From reading briefly about it, it sounds like those individuals are so sensitive to stimuli, they don't leave home for fear of having debilitating spasms from things like car horns. As in, someone beeps their horn and the sufferer falls to the ground. It's not just a matter of being stiff.
Anyhow, you're not alone. I, like strobers, had (and kinda continue to have) a fear of PNE or nerve damage. I realize that it's illogical. I can sit without having to get up, I don't have numbness or tingling, no problem with erections, etc. Nevertheless, because my symptoms are a bit different than the majority, I cling to the possibility. I think it's human nature to expect the worst. The idea of diagnosing oneself with a terrible disease or syndrome is, in a way, very seductive. It allows you to slip away into depression and give up, which is much easier than waking every day and fighting to live a normal life in the face of chronic pain. It's a very difficult battle that we all face. Changing that negativity and self-condemnation is something that seems to be critical to recovery, and I struggle a lot with it.
A big step for me was to swear off medical websites. They serve no purpose but to frighten me. I ended up at the pudendal forums the other night and, naturally, left after having scared the crap out of myself. What good did it do me? None, of course. Just like reading about CRPS or all these other things, all my research did was convince me to be afraid of things I probably don't have.
There are days when I get these sharp, shooting, electric pains in the penis, and they make me panic. I
immediately think PNE or nerve damage. Lately, though, I try to tell myself what another sufferer told me: you've got to live today for today. Tomorrow is another day. You can't change or even know what's going to happen, so there's no point in obsessively worrying about it.
If that seemed long-winded, well, it was intentionally so. Convincing myself as much as I'm trying to convince you.

In the end, there are always options. If you did have Stiff-Person Syndrome, the symptoms of that can usually be well controlled! For strobers and I, if we did have some pain condition related to our nerves, pain management is a field all its own these days. We have many options. Rarely is there a dead end for anything you could diagnose yourself with.
For the moment, though, I would rather not think the worst. I'm trying relaxation, stretching, and hopefully PT if this therapist does the kind of work I need. Trying to stay on the positive side of the fence.