Anxiety is a natural emotional reaction caused by fear or apprehension of distressing events and is very useful for the recognition and response to potential danger. In the absence of real danger, pathological behavioural disturbances caused by anxiety can be continuous or episodic and are often accompanied by physical symptoms. Sleep and concentration disorders have an influence on daily life and are common to different forms of anxiety. People who are affected avoid stressful situations. This avoidance may go so far as to prevent people leaving their homes. Anxiety is a reaction to a real difficulty, but when stress is recurrent, anxiety becomes so extreme that the person is no longer able to react correctly in many areas. Anxiety then becomes pathological, we thus speak of anxiety disorders. Stress is the term originally used for the biological response caused by constraining, unpredictable, new or threatening environmental factors. These biological response triggers are also called stressors; these can be external but also internal, generated by the person themselves. The perception of stress is different according to individuals, nevertheless the functioning of the stress management system (the hypothalamo-pituito-adrenal axis) is the same for everyone. This system increases the production of hormones such as adrenaline and cortisol, to allow the person concerned to react to the stress situation and protect themselves... Stress can be positive by helping concentration, to cope with a period of difficulty but a situation of prolonged stress can have serious consequences for both the psychological and physical health of the sufferer, leading to depression, insomnia and other symptoms.