Didn't really care for the whole acid trip thing. Really just seemed hokey and out of place. Like they just threw that in there for the hell of it. Smh...
Walter has always been on the edge of sanity, and in his case I think the drugs help him keep sane, if that makes sense. Walter is not only fighting the Observers, he's fighting to get back the information they erased from his mind and at the same time fighting to keep the old Walter from taking over.