Reduced concentration, easy fatigability and low energy level are symptoms of depression. With dis if u also have reduced interest in the joyful activities, sleep disturbance, reduced appetite, constant negative thoughts den it is depression. Don't think there should always be a personal reason in u to get this condition. Depression can occur even without any social cause. It's the disturbance in the neurochemical system which precipitate this condition. Certain common medical conditions like anaemia, hypothyroidism, dehydration also known to cause the same symptoms which u ve expressed.