Justin Timberlake is offering an unexpected health update. The SexyBack singer took to Instagram on Thursday to commemorate the end of his controversial Forget Tomorrow World Tour... And to share an explanation for why his recent performances have been so dialed down: "Well, as these two incredible years come to an end and I look forward to the future, I wanted to write something from the heart. It's not an easy task to try to contextualize the whirlwind of touring - but, I will try... This has been the most fun, emotional, gratifying, physically demanding, and, at times, grueling experience.