Being intelligent and aware of everything and then having that intelligence slowly taken away from you, feeling your mental capacity diminishing day by day while still having the awareness that it's happening, it's pretty heavy stuff. It really brings to mind my grandmother's decline after she got Alzheimer's, she was slowly losing herself and for a long time she knew it was happening and it was painful to watch, not to mention how brutal it must have been to experience it.
Flowers for Algernon is an amazing story, but it hits pretty hard after watching it in real life.