When I went for counseling, the Dr. said this about my case: When a person is under a great deal of stress for a prolonged period of time (ptsd) your body will adjust by putting out more of the chemical that helps you deal with it. If this goes on for to long, it will actually cause a physical change in the brain. Once that happens, there is no changing it back. That is when the imbalance comes in. For some, it is just there. For others it is a reaction to overwhelming stress. But there is one thing that we all seem to have in common. We would never wish depression on our worst enemy. It is, indeed, a living hell.