Final answer:
The initial treatment session should include gait training with a focus on starting and stopping, as well as exercises for sit to stand with anterior weight shifting, which are tailored to address the patient's difficulties with movement and balance due to Parkinson's disease.
Step-by-step explanation:
The most appropriate intervention for the initial treatment session for a patient with Parkinson's disease and classified as Hoehn and Yahn III is gait training emphasizing starting and stopping. This approach is directly relevant to the patient's complaint of difficulty turning around and recent falls. Gait training can help improve the coordination of movements required for walking and aid in preventing future falls. Additionally, incorporating exercises that focus on sit to stand with emphasis on anterior weight shifting could be beneficial as it addresses the issue the patient had with getting up off the toilet. A combination of these two interventions can likely provide the most immediate benefit to the patient's functional mobility.