Depression is one of the serious mental illnesses, and the precursors of depression are also called the pre-symptoms of depression, or early symptoms. 13-year-olds can show difficulty falling asleep at night or waking up early, as well as feeling tired and weak doing general activities. Sometimes there is no hunger, no appetite, and no desire to eat, and they may also behave differently than usual, not participating in activities or interacting with classmates, and even when they do participate in social activities, they pretend to be unhappy. Some children may also experience significant distractibility and emotional instability, as well as headaches, lack of energy, memory loss, and mental fatigue. They feel bored and uninterested in everything, such as studying or working.