Sore testicles?

All,
I just tried the Aneros for my first time today (my g/f and I picked it up after months of thinking it looked interesting). She inserted it -very slowly with lots of lube-, I relaxed for a bit, and then we made love.
My orgasm was very intense, and definitely had a different quality, but probably wasn't the "Super-O" I have seen a few mentions of in my quck read of the message board subjects.
After cleaning up, I noticed that my testicles were definitely sore. It is almost exactly like being 18 again and having "blue balls", except that I had a satisfying, ejaculatory orgasm, and there was none of the teasing and long build up that I would have associated with that condition.
Is this normal? Is this something to worry about? Did I do something wrong? While I haven't had a great deal of anal experience, I have inserted a small plug a few times over the years, and even a reasonable sized dildo once or twice. But, this is the first time I have felt any reaction in my testicles.

Any advice or thoughts would be very appreciated.

Censorydep