Final answer:
The person was deeply engrossed in thought, completely disconnected from his surroundings.
Step-by-step explanation:
The person described in the passage was in a state of deep thought and unaware of his surroundings. The text indicates that the person's mind was so intensely focused on organizing complex thoughts that he became oblivious to the physical world around him. This profound absorption in internal contemplation meant that he neither saw, heard, nor knew anything external; his mind took over and transformed his physical existence into something akin to spirit. This sort of total mental engrossment, to the exclusion of sensory perception or awareness of the environment, is associated with individuals who are highly intellectual yet may suffer from periods of morbidity.