There isn't any diagnosis such as " Cyclic depression" as per DSM-IV which is the standard manual used for diagnosing mental disorders. Feeling worthless, sitting in a corner are some of the symptoms of depression. I would need more information regarding your friend's symptoms to come to any reasonable diagnosis as there are several types of depressive disorders. Treatment depends on the particular diagnosis and severity of the condition.
Your friend's diagnosis of "cyclic depression" is more likely to be classified by professionals as "recurrent depression". Another mood disorder sometimes referred to as cyclic dysthymia exists, but has not yet been classified in the DSM-IV. Finally, "cyclothymia" is classified in the DSM-IV as a mood disorder characterized by numerous hypomanic and depressive periods with symptoms like those of manic and major depressive episodes but of lesser severity. Having said this, psychiatry is a extremely complex and evolving branch of neuroscience, and researchers are becoming more aware of the extensive overlap among mood disorders. The Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition (DSM-IV) is generally used only as a guide to clinicians for the purpose of classifying mental illnesses based on signs and symptoms. It is not yet sophisticated enough to differentiate specific mood disorders based on dysfunctions within specific neurochemical circuits in the brain, for example, but it is the best thing we've got so far. "Cyclic depression" may best explain your friend's symptoms for the time being, but the course of treatment is likely to reflect his doctor's clinical experience with his own patients. If you are interested in finding out more, you can search the internet using the keywords "recurrent depression", "treatment resistant depression", "cyclothymia", "depression", "anxiety" and "major depressive disorder" to get a feel for what your friend may be going through. Good luck, and best wishes to your pal,
Your above answer to the cyclic depression is the best answer I have seen to any question I have read on this board. Thanks for taking the time to answer it. It succinctly explains why many of the other answers seem vague. At the same time, it provided much needed information. Thanks again.