The latter chapters are about his childhood, as he has reconstructed it. He was abused by his parents, his mother was borderline psychotic and a pathological liar. His immune system was compromised by years of physical and emotional abuse, which may explain why his brain was attacked by a virus.
In the last couple of chapters his mother develops Alzheimer's, and becomes a sweet if entirely helpless and forgetful old crone. The son muses on whether he'd trade his old foul tempered mother for the one whose memory has been erased.