This is astounding that a sleeping pill could have this effect on people and makes you wonder about any decision to let someone be starved. Starving someone falls into the category of cruel and unusual punishment IMHO and should never happen in this country.
Where there is life, there is always a flicker of hope!
It would not be legal to kill a dog by that method, and neither should it be.
Even if they do not recover, people with severe brain damage often have awareness of things, and can probably feel some sensations, such as thirst.