Depression is a common mental health problem affecting approximately 15% of all individuals. The individual usually suffers from depressed mood, loss of interest and enjoyment, and reduced energy, leading to increased fatigability and diminished activity. Marked tiredness after only slight effort is common. The lowered mood varies little from day to day, and is often unresponsive to circumstances, yet may show a characteristic diurnal variation as the day goes on. Other common symptoms can include: reduced concentration and attention; reduced self-esteem and self-confidence; ideas of guilt and unworthiness; bleak and pessimistic views of the future; ideas or acts of self-harm or suicide; disturbed sleep; and diminished appetite.