I have a runny nose often as well and sometimes get stuffed up when on the toilet, particularly in the mornings...when I was a kid I had nasal issues, always stuffy, couldn't sleep well at night, always tossing and turning, then I got addicted to nasal spray (twice, once as a kid then
again during teen yrs) thankfully I don't get all stuffy like I used to at night and it no longer interferes with my sleep but I'm generally on the runny side now during the day.
I don't know if there's any correlation to IBD or not...and for me I don't think dehydration has anything to do with it...I drink tons of water daily. But who knows.