In my experience, it is often common for people with Parkinson's Disease to develop psychiatric symptoms, especially as the disease progresses. The most common problem tends to be depression, as both the disease itself and the loss of function can lead to this. Fortunately, antidepressants often help with this and are easily tolerated.

Many times, people present as having some Parkinson's disease symptoms, but they can have other symptoms as well. This can include visual hallucinations (especially children) that accompany a dementia. This is called Lewy Body Dementia, and it is very common for these patients to develop psychiatric symptoms. Fortunately, medications can help this as well, but usually an expert guidance is needed, as they tend to be complex patients.