Phillip K Dick's Reality and Manipulation of Senses

I suppose the most impressive thing about Phillip K. Dick's stories is how much he can alter the reality of something without making it completely supernatual. Every single story has one sense or subject that has been manipulated slightly, but it is not totally accepted by the main characters themselves. It reminds me a bit of a particular Twilight Zone episode where a "man" had surgery and was somehow transformed into a "pig-faced" man with an inverted view of life. Thus, when he awoke from his surgery thinking that everyone was "pig-faced" person and that he was the only normal looking human when it was quite the opposite. But this is how Dick's stories work; they take a little piece of the reality you rely and twist it in a way that makes it more fantastic (because it makes one question it). In "Fair Game", the question was Professor Douglas losing it or was there actually an eye out there looking in? Moreover, was the eye really fixated on him or was he just completely off his rocker and imagining the entire thing? "In Let Us Remember It For You Wholesale", the object/sense distorted and heavily manipulated was memory. This is this aspect of the story that really sends the reader on edge. How do we know if something actually happened or not? How does that affect identity? In any case, I believe Phillip K. Dick's work on reality in his stories is absolutely fascinating because it shows just how subjective reality is.