abioticn,
Since you included "bio" and "ticn in your "stage name", as a biologist who
has worked in just about every job a biologist can work in, my wild guess is that you are a Biology Technician?
My first reaction to your plaintive question about "isn't Parkinsons a slowly progressing disease" is this very broad answer:
It depends completely on the individual patient.
Your father may, or he may not, have had some of the less noticeable symptoms of Parkinsons for a very long time before he took a sharp downward turn.
As a pharmaceutical rep in neuroscience for 18 years I was aware that I had Parkinsons for 5 years before I sought treatment.
I only sought treatment, NOT because of tremor, which was barely there, but because of one fall that would have likely killed me if my daughter hadn't grabbed my wrist when I screamed for her to do so, as I was falling backwards onto asphalt.
My only injury was a broken elbow, but that fall was a wakeup call.
For older people, they MAY have what appear to be just a few symptoms for YEARS, like incontinence, trouble finding words, the occasional fall, shuffling gait, difficulty getting up out of their chair, a little trouble with their balance.
These "little" things are commonly associated with the normal aging process and they come on gradually.
At some point they become cumulative and the "little things" coalesce into a diagnosis of Parkinsons.
The progression of Parkinsons can be at a snail's pace for some, like me.
Unfortunately I am the exception not the rule.
There may be someone who can explain WHY some patients progress slowly through Parkinsons and others travel at the speed of light, but I am not that person.
As has been mentioned you need to seek answers from his care team, because your father is their patient and they are the only ones who have answers to your questions.
I can feel your anguish in your words. Do not blame yourself because you certainly did nothing wrong and neither did your father.
Parkinsons is a brutal disease.
We are all here for you ❤ with strength and hope. Thank you for reaching out to us at such a time when things are scary and happening so fast.