I suffered this also, I am not sure what the body is doing but whilst screaming for water and fuel it seems to reject everything. A very experienced running friend told me to try flat cola after the race. It works for me so far.
Seems coke is easier to digest than sports drinks / gels but gives a similar fuel burst. The only time I will ever recommend drinking the stuff.....
I don't get peeps that run on holiday. Unless your top notch elite a week is not going to make much diffrence your body needs a rest once in a while so do it on holiday.
I love running in new places. Whenever i go somewhere either on holiday or work I always try to squeeze in at least one run. Nice to see something new and the software I download the GPS to puts a red dot on the map where I log a run, its great to see the number of different places.