It seems to be the season :(
I came off a few days ago on the way to the office while making a gentler-than-usual turn in a place I've been many times before. It was on a very foggy day and I think the fog had mobilised the grease and crap on the road enough to make it very slippery. Not very pleasing either, really.
Fortunately, the road was closed to most traffic so I had much less risk of being crushed by a bus than I usually would had had there. And it's years since I came off like that too.