it is psychosomatic, but can still be debilitating. i knew a Navy veteran who could not drink straight water at all because while in the Navy, he had to drink several gallons of the stuff every day. as soon as he was discharged (honorably), he found he couldn’t have water without anything added to it simply because he had so much of it in the service. of course, he still has to drink water, so he carries around a bottle of flavoring