Answer: probably 99% of people have experienced some type of Psychological disorder
Explanation: According to the DSM IV-R, the Diagnostic and Statistical Manual that is used to make mental diagnoses, there is a disorder called Adjustment Disorder. Adjustment Disorder is a reaction (fear, anxiety, sadness, depression) that occurs when there is a change in an individual's life that requires an adjustment. Some examples include: moving, changing schools, jobs, new relationships, divorce, etc. My guess is that nearly every person has experienced change at some point in their life and so have experienced an Adjustment Disorder.