Depression is characterized by two things: (1) a sudden drop or loss of interest on the daily activities including those that he or she once enjoyed, and (2) a depressed mood. If one of these two symptoms is present then it's fair to say that the person in question may be suffering from depression, whether they know it or not.

Meanwhile, there are other depression symptoms that may appear in the person...

Irregular sleeping patterns: - A person is expected to sleep during the night for an average of 8 hours a day. However, this may not be possible for a person who is experiencing depression. Changes can be seen if the person is awake for the whole night or could not get enough sleep; he or she could not experience deep sleep and could not go back to sleep when awakened. Irregular sleeping patterns could also mean oversleeping or sleeping throughout the day and staying awake during the night. These irregular sleeping patterns are very common in depressed teens and children.

Loss/gain of appetite: - Some people, when depressed, cannot get the appetite to eat while others tend to gain an appetite particularly for sweets and carbohydrates. As a result, a person who is depressed can either gain or lose a significant amount of weight. Depression that is the result of relationship breakup, divorce, and loss of a relative can have these kinds of manifestations.

Irritability or agitation: - Simple things may cause people suffering from depression to become irritable and easily agitated.

Lack of concentration: - This symptom is more evident to children. A depressed child lacks concentration to focus on lessons. As a result, he or she performs poorly on classes. At home, children manifesting this symptom may appear lost in his or her personal world.

Lack of self-confidence: - This often leads to low self-esteem. As a consequence, the person will develop a fear of other people for no particular reason. He or she would see others as a threat to his or her security. As a consequence, this person will prefer to stay on their own rather than with a group. Depression would then intensify since this kind of isolation is never healthy. Their social skills become compromised and this can lead to future difficulties in forming relationships.

Periods of crying: - Given that a depressed person is sad, he or she could cry with no particular reason. For a depressed child, unreasonable tantrums may become very frequent.

Significant decrease in making love: - The loss of interest in sex and a reduction in libido is very common in someone dealing with depression.

Negative perception towards life and living: - A depressed person may see life as nothing but a waste of time. Some depressed people may even think of committing suicide. This feeling increases if the person thinks that everyone around him or her is against him.

Hopelessness: - When the view of the future is unclear, hopelessness sets in. A feeling that there is no reason to carry on living can grow out of this. This is by far one of the worst symptoms of depression and can cause great psychological damage.

Physical problems: - Emotional distress can cause several physical ailments. This will be more evident in teens and children. Headaches and body pains are more common. Other physical problems such as constipation, chest pain, muscle and joint pain, tiredness, and dizziness can be noticeable.

All these symptoms may be caused by other identifiable physical conditions. However, if 5 or more of these happen all in the same period of time; it seems very clear that the person in question is suffering badly with depression.