1.  Depression is a state of sadness, hopelessness, misery, inferiority, and emptiness, just to name a few.  Someone with depression is usually very critical of themselves, will lose interest in social or physical activities, will disconnect from the world around them, will blame themselves when things go wrong, and will hold a pessimistic view of life's challenges.  A depressed person will also experience loss of appetite and disturbances in sleep patterns.  If feelings of helplessness persist for an extended period of time, perhaps more than two or three weeks, it can be said that the person has unipolar depression.  Unipolar depression has no history of mania.  This means that the person with unipolar depression does not experience episodes of euphoric joy or excitement.  They have no anticipation for exciting things to happen.  
Mania, on the other hand, is a state of euphoria.  Someone with mania will experience strong excitement and motivation to the point that it is not coherent or in touch with reality.  They experience a dramatic increase in energy and mood.  They are physically active and feel they can do a lot of things without getting sufficient sleep.   They feel like they can conquer the world.  They can make impulsive decisions and become easily angered if someone gets in the way of what they are trying to achieve.  The manic person has an inflated ego and wants to get involved in risky situations.  Individuals with full manic episodes that lasts more than a week or two and have major depressive episodes are diagnosed with Bipolar disorder.  In Bipolar disorder, the person has dramatic highs and lows that disrupt their daily living and robs them of having healthy, stable relationships.