How? Or is this more of a case of "To the extent of my ability to reason about my own state of being, I'm conscious. But I can't reason about external entities."
There's a pretty hefty literature tackling that claim, ranging from stuffy academic treatises to Nietzsche:
There are still harmless self-observers who believe that there are "immediate certainties"; for example, "I think," or as the superstition of Schopenhauer put it, "I will"; as though knowledge here got hold of its object purely and nakedly as "the thing in itself," without any falsification on the part of either the subject or the object. But that "immediate certainty," as well as "absolute knowledge" and the "thing in itself," involve a contradictio in adjecto," I shall repeat a hundred times; we really ought to free ourselves from the seduction of words!
Let the people suppose that knowledge means knowing things entirely; the philosopher must say to himself: When I analyze the process that is expressed in the sentence, "I think," I find a whole series of daring assertions that would be difficult, perhaps impossible, to prove; for example, that it is I who think, that there must necessarily be something that thinks, that thinking is an activity and operation on the part of a being who is thought of as a cause, that there is an "ego," and, finally, that it is already determined what is to be designated by thinking--that I know what thinking is, For if I had not already decided within myself what it is, by what standard could I determine whether that which is just happening is not perhaps "willing" or "feeling"? In short, the assertion "I think" assumes that I compare my state at the present moment with other states of myself which I know, in order to determine what it is; on account of this retrospective connection with further "knowledge," it has, at any rate, no immediate certainty for me.
In place of the "immediate certainty" in which the people may believe in the case at hand, the philosopher thus finds a series of metaphysical questions presented to him, truly searching questions of the intellect; to wit: "From where do I get the concept of thinking? Why do I believe in cause and effect? What gives me the right to speak of an ego, and even of an ego as cause, and finally of an ego as the cause of thought?" Whoever ventures to answer these metaphysical questions at once by an appeal to a sort of intuitive perception, like the person who says, "I think, and know that this, at least, is true, actual, and certain"--will encounter a smile and two question marks from a philosopher nowadays. "Sir," the philosopher will perhaps give him to understand, "it is improbable that you are not mistaken; but why insist on the truth?"
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With regard to the superstitions of logicians, I shall never tire of emphasizing a small terse fact, which these superstitious minds hate to concede--namely, that a thought comes when "it" wishes, and not when "I" wish, so that it is a falsification of the facts of the case to say that the subject "I" is the condition of the predicate "think." It thinks; but that this "it" is precisely the famous old "ego" is, to put it mildly, only a supposition, an assertion, and assuredly not an "immediate certainty." After all, one has even gone too far with this "it thinks"--even the "it" contains an interpretation of the process, and does not belong to the process itself. One infers here according to the grammatical habit: "Thinking is an activity; every activity requires an agent; consequently--"