Homeostasis is an (ideal or virtual) state of equilibrium, in which all body systems are working and interacting in an appropriate way to fulfill all the needs of the person and/or the body.
When homeostasis is interrupted (e.g. by response to a stressor), the body tries to restore it by adjusting one or more physiological processes. This stress-adaption mechanism includes activation of the Hypothalamic-Pitauitary-Andrenal Axis (HPA Axis) with the autonomous nervous system and endocrine reactions of the body.
Severe stressors or long lasting adjustment demands can cause severe imbalance of this steady state. This might cause not only psychological distress but also psycho-somatic disorders.