This was a well know fact in art school. Usually a student and teacher would drive themselves for days to finish a project/painting/sculpture and then go into a mental physical funk for days after it was finished certain that the completed project was a failure and that inspiration would never strike again. Then the process would be repeated. Almost without exception at the school I attended all the successful students and teachers who did creative work - work which was not built on work or ideas of others - went through this process. The manic/depressive stages were more pronounced for some than others and some were under doctors care and some self medicated with drugs and alcohol. Some didn't.