Answer:
Feeling down or depressed is when you experience sadness like any other person and once you are done you move on in your life.
Depression is a disorder that is almost like a black cloud over you and you don't move on from that sadness you stay stuck in that place and you experience seclusion, loss of interest, et cetera. Here is the dictionary definition of Depression:
feelings of severe despondency and dejection.
And Sadness is:
feeling or showing sorrow; unhappy
Explanation:
The main difference in these two definitions is the way in which they are described, depression is much more severe than sadness.
