Tried that as a teenager. Obviously didn't work. After a couple days, I did not experience intense thirst anymore and felt very sleepy + weaker and weaker. As far as I can recall, except for the dry mouth and throat, it was not that unpleasant. Then it's very blurry, but I can remember my thoughts were very altered and confused, so I can well imagine that some would experience hallucinations (that wasn't my case at that point though). I was eventually admitted in an intensive care unit where I was dripped. I think I still had some time before I'd experience the actual documented agony of this method, so I was probably still very far from death.
I don't think it's a peaceful way to go at all. Very unreliable, very slow, and probably very painful at some point. Unless you live as a complete recluse, it's very likely that you'll be saved long before you're at the slightest risk of dying.