Hypochondria is a mental disorder characterized by an irrational and chronic worry about one's health. It's usually linked with obsession and depression, and patients typically suffer from imaginary or exaggerated illnesses.

Hysteria, or conversion disorder, is characterized by a major change in physical functioning that can't be explained by a physiological cause. The symptoms aren't fake or intentionally produced, and generally appear suddenly in stressful situations.

Stress generally occurs when your life demands that you adjust, cope, or adapt to new situations. Although you deal successfully with some degree of stress every day, excessive stress can sometimes be difficult to overcome.

Stress generally occurs when you have to adapt, cope, or adjust to a change in your environment. In most cases stress is reasonably proportional to the event that triggers it.