I think it may be a bad idea to use such an old post, but I wanted to say that for my POIS (which type I don't know) I also suffer Dehydration, and drinking doesn't solve it. But in my case it may be related to some digestive problem I don't know; it seems I also have Lactose Intolerance or something similar as eating dairy stops my stomach and causes diarrhea (strangely, pois also seems like causing me some kind of stomach stop). I can distingish between them, because if its milk I use Lactase (Enzyme) and cures and prevents the milk induced problem, but not the POIS induced digestive problem.
Regarding the Dehydration, I said that it may be digestive, but I think is more probable that some hormonary thing is affetced, because drinknig more water, leads to more urination (I'm not 100% sure), it doesn't solve the Dehydration; it's like using diuretics.
In my case theese dehydration symptoms appear hours after ejaculation, and dissappear 1 day or more after. (I think Depression, brain fog, concentration problems, and other effects remain more time)
Anecdotically, when I'm feeling down I have a strange impulse to do caresses, or be caressed; and also a craving for romantic stories (I never had a partner). Tipically I don't read romantic stories in that moments, because I feel too depressed and with a desmotivational blocking to do anything.