The onset of depression can be brought on by psychological, physical or social causes, or indeed a mixture of these, and therefore the subject is complex and varied. 
Depression will affect at least 1 in 3 people during their lifetime so you are certainly not alone in this. 
The initial signs of depression can be simple things such as changes in eating habits or sleeping patterns. Low moods often lead to periods of despair. You may become emotionally detached from loved ones, friends or relatives which lead to a feeling of isolation.
Other symptoms can be:
  • Lacking energy or feeling tired.
  • Feeling restless or agitated
  • Tearful
  • Not wanting to talk or avoiding social situations
  • Not doing things you usually enjoy
  • Using alcohol or drugs to help cope
Extreme or prolonged depressive feelings can lead to overwhelming thoughts of self harm or even suicide. This doesn't mean necessarily that you are likely to carry these things out but obviously these are major warning signs.  It is important that you do not ignore the symptoms
Remember depression is an illness that can be treated...there can be an end to this for you