Parkinson's disease is a condition in which parts of the brain become progressively damaged over many years. The three main symptoms of Parkinson's disease are: involuntary shaking of particular parts of the body (tremor) slow movement stiff and inflexible muscles A person with Parkinson's disease can also experience a wide range of other physical and psychological symptoms, including: depression and anxiety balance problems – this may increase the chance of a fall loss of sense of smell anosmis problems sleeping (insomnia) memory problems