anxiety 

The group of anxiety disorders include general anxiety (or what is known as "free floating anxiety"), panic, post-traumatic stress, phobias and obsessive-compulsive disorder. It may affect your social life by making it too nerve wracking to attend social occasions, it may affect your job when you have to attend meetings or give presentations or it may manifest itself in other situations such as being too scared to fly so that you
are unable to go on foreign holidays or, in more extreme cases, even leaving the house.  

It is possibly best to think of it as a normal response which has become too extreme or got out of control. For instance, it is not uncommon for any of us to double check that we have turned the lights off before we go out. For an obsessive-compulsive person, however, the anxiety that the lights have not been turned off may be so overwhelming that it is almost impossible to leave the house at all. 

Anxiety can affect us physically as well as emotionally. We might break out in a sweat, experience pains in different parts of our body,
even think that we are dying. We might also feel very helpless and be constantly worried that something awful is going to happen or be
constantly irritable and watching for an imagined dreaded event. This can have long term effects on health and cause problems
associated with increased blood pressure and a lowering of resistance to illness. 

The causes of anxiety are most likely to be found in a mixture of upbringing, personality and current life circumstances. It may be a "learned response" in that in the family there was always a feeling that the outside world was a threatening place or the individual concerned may never have developed a sense of personal autonomy and security.