@ttyymmnn Everybody'd situation is different but head droop was what triggered our inquiry into working on dad's dosage. That got me talking to my cousin and learning that you need to really work with the dosage over the progression of the disease. We increased dosage and it helped. Simply put, dad was taking a lot less medication than what he needed.
Droop is what the medication is intended to fix. I suggest talking to his doctor and try different dosage levels and also a mix of slow acting and fast acting.
Unfortunately Dad's first doctor was a nurse practitioner who had little experience with Carbidopa. She gave dad a standard "learner's" dosage and never followed up. We got my dad into my cousin's doctor who was an Parkinson's expert and he encouraged us to find what worked for dad.
Carbidopa is really good stuff, but it takes active management to get the most benefit. I think most doctors prescribe 30% the needed dosage because they don't have the time to fine tune it. In my assessment 30% gives 25% (or less) the benefit with no risk or needed follow-up.
I wouldn't be ok with 25% the benefit if that means drooping for the afternoon. You might as well make the most of it, so if the doctor is not helping you, go find another that will work more closely.
By the way, drooping is not the only issue with poorly managed Parkinson's. It also causes decreased swallowing ability that gives you aspirational pneumonia which is what kills many with Parkinson's. So one other thing is I would be actively be looking for choking issues. If he is coughing while and after eating, you may need to look at grinding his food.
My dad got pneumonia 6 months before he passed. He considered his choking ot be no big deal. Well the pneumonia took a lot out of him was the start of his long decline. He had pneumonia twice and after each case, his Parkinson's took a big step change increase of symptoms.
In his first case he walked out of the house with pneumonia and after a 2 week Pneumonia stay, never walked unassisted again. So if your dad is choking on his meals, its best to be proactive.
Ps, what I believe got my dad ultimately was not Parkinsons but a large slow growing brain tumor. As for parkinson's, both my cousin and his dad have both lived well with Parkinson's for going on 15 years.