My Elderly Friend Became Dehydrated From What We Thought Was

My elderly friend became dehydrated from what we thought was a stomach virus.3 days later and no food eaten he was taken to the ER because he suddenly became totally dehydrated and mentally confused and talking gibberish. His blood levels are good. He was diagnosed with dehydration, low potassium and Ut infection. They have a endoscopy scheduled in 2 more days once he is more stable. He vomits or regurgitates dark brown liquid constantly. So far they have no idea why. Can you help me? Thank you.