Depression is a state of low mood and aversion to activity. It can affect a person's thoughts, behavior, motivation, feelings, and sense of well-being. It may feature sadness, difficulty in thinking and concentration and a significant increase/decrease in appetite and time spent sleeping, and people experiencing depression may have feelings of dejection, hopelessness and, sometimes, suicidal thoughts. It can either be short term or long term. Depressed mood is a symptom of some mood disorders such as major depressive disorder or dysthymia; it is a normal temporary reaction to life events, such as the loss of a loved one; and it is also a symptom of some physical diseases and a side effect of some drugs and medical treatments.