DEPRESSION
Depression comes in many forms. People experience depression as a
reaction to situations. It is a normal part of life and if we are  honest
with ourselves we will  remember times we've been depressed.
Depression is a normal response to certain situations:
loss of a loved one (and, yes, pets count),
changes in life situations e.g. divorce, moves, decline in health, etc.
Sometimes depression is caused by chemical changes in the
brain and may be helped with medication. But even for those
individuals medicine alone will not cure the condition.
Perhaps you are reading this because you are currently experiencing
depression and you are wondering if it is normal, and when will it end.
Talking does help.
Some signs of depression