Weight loss, weakness, and digestion problems like loose motions and poor appetite are common in Parkinson's, but they need attention. These could be due to the disease itself, medicines, or nutritional issues. Focus on small, frequent meals, easy-to-digest foods, and adequate fluids, and talk to your neurologist, they may adjust medicines or suggest nutrition support.

What your father is experiencing sounds like the wearing off or medication side effects of Syndopa and Rasalect, which are common in long-term Parkinson's treatment. Do not change medicines on your own, as sudden changes can be risky. Please consult his neurologist, who may adjust the timing or dose of current medicines.