In general, someone is in a crisis when the stresses they are dealing with overwhelm their ability to cope.
Stress can take the form of any challenge or hazard.
People deal with stress by using problem-solving, social support, relaxation, and other coping skills. Usually there is a balance maintained between the level of stress and one's coping efforts. A crisis occurs when this equilibrium is disrupted. Like a struggling swimmer who panics and grabs the lifeguard around the neck, or the depressed person who drinks more alcohol, a person in crisis often loses perspective and the ability to solve problems in organized and realistic ways. As a result, friends of the person in crisis often feel new demands and challenges in their relationships.