What is that one disease which has taken almost all the lives on the planet in its grip? Depression. In a survey it has been confirmed that depression is the most common disease that everybody is suffering from. But it is not limited to just this. Depression and anxiety could be the symptoms leading to Parkinson's disease says doctors on the occasion of World Parkinson's Day. What Is Parkinson’s Disease? Parkinson's disease is a progressive nervous system disorder that affects the movement of the human body. Symptoms start gradually sometimes starting with a barely noticeable tremor in just one hand.