To diagnose Parkinson's disease, one or more of the four most common motor symptoms must be present (primary motor symptoms). In addition to that, there are many secondary and nonmotor symptoms that doctors use to recognize, diagnose and manage PD. However, in the early stages of PD, the symptoms may be so mild that they go unnoticed.

Each PD patient will experience the symptoms differently at various degrees of strength. The disease will progress very quickly for some, but slowly for others.

Most patients experience severe symptoms on one side of their bodies for years. However these symptoms will progressively become evident on the other side of the body, but will not be as severe as they are on the initial side.  

Source: http://www.pdf.org/en/symptoms