I have a close family member who was diagnosed with Parkinson's around 20 years ago. It can be pretty frightening towards the end, but it's possible to maintain a relatively high degree of function/quality of life for several years after diagnosis, with the appropriate treatment.
I would consider ALS to be the most frightening though, due to how rapidly it advances.
I would consider ALS to be the most frightening though, due to how rapidly it advances.