LOS ANGELES, Calif. -- Simon Cowell may appear confident as he sits behind the judge's booth on 'American Idol,' but he revealed he has some very dark times.In a letter to his 'shallow, reckless, cocky younger self,' to celebrate his upcoming 50th birthday on October 7, Simon revealed he suffers from 'black moods.''Sometimes, when friends are over, you want to ask them to leave. You get hit by black moods and you want to be alone,' he writes in the lengthy letter, printed in the U.K.'s Daily Mail on Monday.