Sinemet can give sleepiness when kicking in. I would not call it an 'off' but more of a wearing on or off phenomena.

Sinemet can actually cause increased urination.

Sinemet at night can make a person wakeful.

Dopamine replacement is tricky and difficult to manage and very individual.
I guess you are finding out just how true this is.

I would second others in saying that good diagnosis is really important. No one who does not need it should be on these drugs.

There is a tendency for doctors to tinker with levels of medication because really what else have they to do?

The patient is the one who usually has to manage to find the tightrope path of dosage that works for them, by trial and error. This can take a long time. In an elderly person this is difficult, especially as time becomes more precious.

I think you have got some of the aspects of what these drugs do covered, in that you understand that some of what you are seeing is side effect, and some is your mothers condition. Having lowered my dose in the past, I would say that the schedule that your doctor has given is optimistic, and slower would be better, but this is only my personal experience.

You need to work with your mother on this to get her to as comfortable place as possible. That is the best that can be said. Use the doctors instructions as guidelines, but back off if she is having a worse day and go a little slower. She has an older, and therefore more fragile brain.

Best of all get another opinion, the best you can find. And if possible document what you are seeing. If your mother can do this too, it might also be useful.

She could possibly have an age related parkinsonism rather than IPD?

Good luck with finding a way to resolve these issues.