What is the theme in The Man Who Mistook His Wife for a Hat and Other Clinical Tales by Oliver Sacks?

One of the themes that emerges is the possibility that Sacks' patients are not truly "sick." Often the reader gets the impression that the so-called "affliction" from which the patient suffers has actually enhanced the person's life. Quite possibly the disease enables the patient to live a fuller life and do things he or she may not have done otherwise.