I've never, and would never abstain from drinking (too afraid), but I've often tried starving myself, and my experience is that it's very unpleasant. It's painful, a kind of pain different from pain caused by injury; it's more dull and low-level, but nonetheless very irritating and impossible to ignore. I have only ever starved for several days, I imagine that the pain worsens but I don't know. Mentally, I find it extremely torturous. The brain is pulling all sorts of tricks during a time of food scarcity, in order to motivate the seeking out and consumption of food. Despite all of this, I'm still illogically drawn to it as a method.