Coping with fall depression

Quite often many of us suffer from fall depression. You become sluggish and low motivated. Nothing inspires you and you want do nothing except sleeping and nagging. You become more vulnerable and irritated. You are not okay with so many things and you feel yourself desperate. Another common symptom of fall depression is eating disorder. You crave for unhealthy foods or do not want to it at all. It seems like everything is okay but anyway it doesn’t make much sense for you. What are actual reasons of this state? Why do you feel yourself depressed and frustrated? And what should you do to cope with it?