To say that you knew that you did not know does not make much sense. This implies that you had a consciousness, but it was covered by some peculiar veil. You may ask me what this veil is made of, and why it is harassing and covering you like that. This veil is constituted of desires. Every human being has desires.
Fulfilled desires produce impressions, and they act like a cloud on consciousness.
Unfulfilled desires are still worse. If you know something of psychology, you will know that the mind has various strata the conscious, subconscious and unconscious level, etc. The unconscious level also is a kind of mental level only. These are all forms taken by unfulfilled desires. This is the reason why you are not really conscious of your existence in the state of deep sleep, and you are only inferring afterwards that you slept, though you did know what it was all about.