Initially thought I'd accidentally eaten some garlic and had an allergic reaction, but due to the fact this lingered more than 24 hrs probably meant it was something else.
May have picked up a stomach bug from the water & may have been suffering mildly earlier but competing exacerbated the situation. It certainly made things noticably worse on Monday & Tuesday evening/afternoons, as did over-hydrating to try and get drug testing on Monday after the race over in done with in time to get Aoife home for bed :(. No-one else got anything so unlikely to be food related. Still not eating Friday lunch, but perfectly fine by dinner :).