Everybody experiences feelings of anxiety. It is a normal and natural reaction to something seen as threatening. It is the emotion felt when in a tight corner, under stress or when facing physical, emotional or intellectual danger of some sort. Individuals may constantly experience feelings of tension and anxiety. These include feelings of apprehension, an inability to concentrate, sweating, shakiness, muscular twitches, and restlessness. Obsessions are fears fuelled by persistent, unwanted thoughts that keep recurring, despite resistance or knowledge that they are ungrounded. The vicious anxiety chain occurs when feelings of anxiety build up to such a pitch that they begin to get out of all proportion to the situation. Anxiety cannot be passed on to another person in the same manner as a virus. However, a vulnerability to fears and phobias can run in the family. Physical treatments, such as electro-shock treatment or psychosurgery, are normally used only in the most extreme cases and usually there are additional problems.