I think most people get this over long distance. It's a mixture of you drinking a lot of fluid, coldness, your body getting physically and mentally tired, and overindulgence in caffeine, which is a diuretic. I can do a 200km without a problem, but much further than that and I start needing regular comfort breaks. That's on an upright, I've not ridden any distance on a 'bent.
PS, the guy who broke the 24hour record on a recumbent had a camelbak rigged up to pee into. You'd have to be careful not to get the hoses mixed up though...