In psychology, stress is a feeling of emotional strain and pressure. Stress is a type of<unk>  pain. Small amounts of stress may be beneficial, as it can improve athletic performance, motivation and reaction to the environment. Excessive amounts of stress, however, can increase the risk of strokes, heart attacks, ulcers, and mental illnesses such as depression and also aggravation of a pre-existing condition. Stress can be external and related to the environment, but may also be caused by internal perceptions that cause an individual to experience anxiety or other negative emotions surrounding a situation, such as pressure, discomfort, etc., which they then deem stressful. Hans Selye (1974) proposed four variations of stress. On one axis he locates good stress (eustress) and bad stress (distress). On the other is over-stress (hyperstress) and understress (hypostress). Selye advocates balancing these: the ultimate goal would be to balance hyperstress and hypostress perfectly and have as much eustress as possible. The term "eustress" comes from the Greek root eu- which means "good" (as in "euphoria"). Eustress results when a person perceives a stressor as positive. "Distress" stems from the Latin root dis- (as in "dissonance" or "disagreement"). Medically defined distress is a threat to the quality of life. It occurs when a demand vastly exceeds a person's capabilities. Stress may cause headache.
Psychological stress
Social stress
Incident stress
Psychological trauma
Chronic stress
Stress 
Drug withdrawal
Opioid-induced endocrinopathy