The type of mental illness in which the patient displays abnormal behavior is called a mental disorder.  When the person experiences a depressive episode only, then it is called a unipolar disorder.  When the episode occurs between the two poles of depression and mania, it is called  bipolar disorder. Thus both unipolar and bipolar disorders are disorders which have varying affects on the patient.

New studies have revealed that there are subtle differences between these disorders. In comparative studies between unipolar and bipolar disorders, it was found that women are more prone to suffer from unipolar disorder and at a later age while bipolar disorder appears to be more prevalent in men and the average age group is late adolescence and early adulthood.  In unipolar disorder, there is insomnia and it is very difficult for such a patient to fall asleep.  He/She mostly experiences stressful sleep and waking up often during the night.  In bipolar disorder, the symptoms are excessive sleep, tiredness and great difficulty in waking up in the morning. 

Further comparisons between unipolar and bipolar patients reveal that  unipolar patients suffer loss of appetite.  A bipolar patient would experience excessive craving for carbohydrate or severe loss of appetite.  A unipolar patient is prone to feeling very active, aggressive and very restless but a  patient with bipolar disorder shows complacency, very inert, very slow with movements and very solemn. In unipolar disorder, the mood episodes are personified by despondency, unworthiness and with no sense of hope.  In a bipolar patient, the symptoms are the same along with psychotic characteristics like hallucinations, etc.

Unipolar patients are able to respond to treatment much faster.  Since it is associated with a single causative factor, it is easier for the doctor to isolate the symptom and diagnose the condition correctly, hence, recovery is fast.  Given the complexity of mood episodes in bipolar disorder, identifying the type of the bipolar disorder itself is a long drawn out process. Once the type of  bipolar disorder is determined, the doctor can begin the process of treating the  patient.  Moreover, the solutions for both unipolar and bipolar disorders are neither permanent nor a quick-fix.  

One other point of comparison between unipolar and bipolar disorders is that though both revealed that the impact of episodes did have bearing on the outcome, bipolar patients were often prone to suicidal tendencies along with rage, sadness, restlessness and low self-esteem.   Unipolar patients never showed the extreme despondent tendencies of suicide but they manifested constant fatigue and tiredness which did not exist in the bipolar patients.  They were in fact, hyperactive.

Unipolar and bipolar disorders are mental illnesses that have ever lasting consequences in the lives of patients.  The degree of suffering may be a little less in a unipolar patient as compared to a bipolar patient. Moreover, the reasons and causes for these disorders are common - genetic defects, environmental influences like stress and substance abuse.

Resources:

http://www.angelfire.com/home/bphoenix1/uni.html