Creutzfeldt–Jakob disease (CJD) is a universally fatal brain disorder. Early symptoms include memory problems, behavioral changes, poor coordination, and visual disturbances. Later dementia, involuntary movements, blindness, weakness, and coma occur. About 90% of people die within a year of diagnosis
As said by this nurse (reddit user elshad85):
I’m a hospice nurse. I’ve seen lots of shitty ways to die, but Creutzfeld Jakob disease scares the shit out of me. One day you are ok, the next your having a hard time walking, maybe a little weak. Within a few weeks to maybe a few months things spiral downwards, you are less able to move, you start falling, you get anxious, your memory starts to sputter, and no one knows what’s going on. 2 to 6 weeks before you die (or maybe much closer to your death) someone hypothesizes that maybe, perhaps you have a prion disease. Nothing they can do until you’re dead and can cut your brain open to be sure. In the meantime you become psychotic, agitated, and have pain in your head (the neurologists will tell you this doesn’t happen, but my clinical experience leads me to believe otherwise). Finally, you die, and your family is left wondering how the hell this happened to a young, healthy person so quickly.
Truly horrible, like dementia in super fast forward mode for younger healthier people.