Symptoms of depression include long periods of sadness, fatigue, changes in sleeping or eating patterns, loss of interest or enthusiasm, feelings of deep unwarranted guilt, and suicidal thoughts.
Sadness, however, passes with time, can be brought on by a number of life events, has links to a specific trigger, and can be somewhat relieved by things such as crying, venting, or talking out frustrations.
Hope this helps!! :)