I also vote for dehydration.
You might try drinking an electrolyte beverage or broth. Salt in either beverage will help you to retain fluids. When engaging in long distance through-hikes I always drink Vitalyte. It's the best hydrating beverage I have found for my revised plumbing. You can read more about it at www.vitalyte.com The product was developed by a chemist/Olympic runner.
dx proctitis in 1987
dx UC in 1991, was stable until 1998
1998 started prednisone, asacol, pentasa, nortriptylene, ativan, 6MP, rowasa enemas and suppositories, hydrocortisone enemas, tried the SCD diet, being a vegetarian, omega 3s, flax, pranic healing, yoga, acupuncture, probiotics
2000 lost all my B-12 stores and became anemic
2001 opted for j-pouch surgery- now living life med-free