There are many causes for depression, for example you may have suffered a loss, been made redundant, be suffering from post-natal depression or possibly suffer from a bi-polar disorder. Some of the symptoms of depression are:
feelings of helplessness and hopelessness
feeling useless, inadequate, bad, self hatred, constant questioning of thoughts and actions, an overwhelming need for reassurance
being vulnerable and "over-sensitive", feeling guilty
a loss of energy and motivation, that makes even the simplest tasks or decision seem difficult
self harm
loss or gain in weight
difficulty with getting off to sleep, or (less frequently) and excessive desire to sleep
agitation and restlessness
loss of sex drive
finding it impossible to concentrate for any length of time, forgetfulness and a sense of unreality
physical aches and pains, sometimes with the fear that you are seriously ill
In more serious cases of depression these feelings may also include:
suicidal ideas
failure to eat or drink
delusions and/or hallucinations
You should always seek the advice of your GP since depression may be symptomatic of other issues that may have a physical cause. Treatment for depression may include prescribed anti-depressants or other medication. Generally counselling and/or psychotherapy can very positively assist in either managing or even resolving depression. Psychotherapy may be short (up to 12 months) and focussed (e.g. CBT which could identify and then seek to change the negative thoughts and feelings affecting behaviour) or longer term focussing on relationships, past experiences with a focus on expressing feelings so that original solutions may be found which may be only applicable to that individual.