What has happened to critical analysis? We need to look a little closer:
The most obvious question to be answered before any progress can be made is simple: what is energy? In the last 40 years, the term has been hijacked by philosphers, new agers, religions, cults to serve whatever purpose. There is nothing inherently wrong with the adoption of new meanings for a word with its scientific origins in the 300-year old writing of Newton, who gives it a very specific physical meaning. The problem that arises is there becomes a confusion when energy is considered across disciplines, and in this case it seems as though it is being used to evoke some sort of spiritual meaning that supposedly we should already understand.
According to your admittedly brief synopsis of Castenada's work, he states that the universe and everything in it is either energy or the absence of it. Thanks to the Special Theory of Relativity we can wholeheartedly agree with that from a physical standpoint and contention from within the scientific community would be few and far between. If, though, he argues that this is the same energy that one gains from eliminating unnecessaries from life then that is a striking fallacy and he is preying upon a symantic weakness of the English language. In other words, without a clear definition of terms, axioms, and premises, deductive syllogistic reasoning fails to lead anywhere.
So what is energy?
Perhaps in this case energy represents a greater hold on our intrinstic physical senses. I agree that withdrawal from unnecessary interactions would and does heighten personal awareness and the acuteness of the senses. To assume, however, that at some point they become so finely tuned as to allow them to operate in an entirely different fashion, ie omniscient perception of time, space, and other living organisms does not readily derive from anything. It is mere speculation, and in fact speculation is far too honorable a term for something without any basis whatsoever.
So take that, man with disputed doctorate in anthropology.