I think it was just a series of them, hit a part of road that resembled Roubaix at speed. Come to think of it, the mud up my back may not be mud....
Moving on, around here it is mainly drains that are the culprit. Probably because we just cover the old road with new tarmac, so the drains are about 4 inch drops. I did hear a prang coming from my back wheel, but I thought that if I stop and investigate I will end up walking just in case. I was about 20 miles away from home and didn't have a clue where I was so just tentatively carried on waiting for the next thing to bugger up.