It is a natural part of life to feel low, worried, sad and listless now and again. Sometimes certain events can make you feel low. You may often feel low without anything in particular having happened. A low mood almost always lifts by itself, but it can take time.
Feeling sad and low or temporarily out of balance is common and is something that affects everyone. It is a part of life. But if you experience a lengthy period of feeling low and hopeless and feelings of meaninglessness, you may have developed depression.