There is a problem, however. Logically (metaphysically) existense precedes both consciousness and the unique human consciousness capable of thought. Epistemologically, the concept of existense, that which we are conscious of, precedes concepts that could question it. If the concept of existense itself is questioned, there is no epistemological basis for doubt, which is a negation of assertion. If nothing is asserted, there is nothing to doubt. If nothing exists, there is nothing to question. To question existense is an example of the "stolen concept" falacy. Existense, not just the concept, must be assumed to question it.
Hank
Therefore: "I am, therefore I think".
............which is the opposite of Descartes' famous philosophical aphorism: "I think, therefore I am".