How do you know if you just have the blues and are experiencing a sad period of time in your life or if you are having a real depressive episode?

The guidelines for the distinction between these two descriptors are clearly stated in the DSM or Diagnostic and Statistical Manual, a publication of the professional mental health community.

The main way to distinguish the difference would be to determine if you have felt sad/empty or felt a loss of pleasure/interest  in the things that have usually brought you pleasure.  Ask yourself if you have felt either of these two symptoms  for a period of two weeks or more. 

 Other indicators could be:

              A significant weight loss or gain

              Trouble  sleeping  as in falling asleep or staying asleep throughout the night

              People  around you noticing that you have slowed down or sped up considerably

              Feeling  fatigued, without energy almost every day

              A feeling of worthlessness or excessive guilt nearly every day,

              Difficulty thinking,  concentrating,  making decisions,

             Recurrent  thoughts  of death or suicide with or without a specific plan.

Sometimes it is difficult to evaluate these symptoms on your own.   Other people including friends,family,co-workers can observe them more objectively than you.  If you have any concerns , it can be helpful to discuss this with a therapist.  Depression is something that can be treated.  You can get your life back.