Pop star Justin Timberlake told fans Thursday he has Lyme disease, a condition he described as "relentlessly debilitating."

The 44-year-old former NSYNC frontman, whose world tour has just wrapped up, took to Instagram in reflective mood.

"This has been the most fun, emotional, gratifying, physically demanding, and, at times, grueling experience," he said of a tour that was criticized by some fans as lackluster.

"Among other things, I've been battling some health issues, and was diagnosed with Lyme disease — which I don't say so you feel bad for me — but to shed some light on what I've been up against behind the scenes.

"Living with this can be relentlessly debilitating, both mentally and physically. When I first got the diagnosis I was shocked for sure. But, at least I could understand why I would be onstage and in a massive amount of nerve pain or just feeling crazy fatigue or sickness."

Lyme disease is caused by a bacteria often carried by ticks that live in woodlands throughout North America and Europe.

Symptoms can include widespread pain, fatigue, and muscle weakness. In serious cases, patients could experience damage to the tissues, joints and immune system.

The "Can't Stop The Feeling" singer was in legal hot water last year after being arrested for drunk driving in a small town near New York.

Timberlake, whose tumultuous relationship with Britney Spears was the inspiration for his 2002 smash "Cry Me A River" later pleaded guilty to a lesser charge and was ordered to do community service.