Sorry to hear this Dan. It sounds very similar to how i crashed my zed, as others will clarify I was not doing anything stupid at the time and going round a roundabout just lost control and was not able to get it back under control enough before clipping a kerb and shooting across a dual carriageway into the barrier. I was the same as you, I felt i was a fairly good driver and felt i knew how to control the car. I guess if i was not as confident behind the wheel as i was the accident could of been a lot worse. I would guess you did everything that is humanly possible to control the outcome and you just have to put it down to the fact that we can not control everything. Even racing drivers with hours of experience have accidents!
I am still to this day very weary of damp conditions and always in the back of my mind that it could quite easily happen again. You could drive the rest of your life without it ever happening again or it could happen next week, its just bad luck. Do not beat yourself up about it, it proves one thing and that you are actually only human. Im glad you were not injured and the car has now been fixed. Im sure in the long run it will make you a better driver.