“Pillowman” descends vertigo-inducingly from a set, as unbalancing as its characters, both too humored and too real for a dark comedy. Combined with an inevitability reminiscient of “Postman Never Rings Twice” and “Dead Like Me”, intermission wonders how the play could ever be viewed completely through, much less multiple times, until after it’s over the wonder of the horror is not only accepted, but understood.