My father, who has brain cancer, said after coming out of surgery that he felt he was at about 75% of capacity. It's funny, as far as deadly serious cancer goes, that immediately before he said that, I thought to myself - but didn't say aloud - that he was at about 70%, compared to 10% before going into surgery.

Anecdotal evidence is anecdotal, but not all brain damage renders one unaware of its presence.