Richard Simmons has disappeared from public view this year with entertainment websites Thursday reporting him to be extremely depressed and incommunicado.

The fitness maven, who spent a career in highly public view, last appeared publicly for a charity event on Jan. 11.

Simmons reportedly doesn't return phone calls and messages, even from those near and dear. He hasn't been seen at his Beverly Hills studio for months. His maid won't let people inside the home when they come to call.

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Some Sources close to Simmons said he was suffering from massive depression stemming from right knee replacement surgery he underwent in 2010. He put off the needed surgery for 10 years, fearing he wouldn't be able to exercise properly.

Simmons also tried red blood platelet and stem cell therapy for his bad knees, similar to treatment that worked out for basketball star Kobe Bryant. However, those treatments didn't seem to help. The latest bad news for him came in the form of his left knee now needing replacement surgery.

That apparently sent him into a depression spiral due to fears his exercising days were over should he not get the surgery. And he doesn't want the surgery.

Knee surgeries aside, other sources close to Simmons told TMZ and other tabloid media the depression ran deeper still, not even related to the surgery but to lifestyle questions. TMZ tried to contact Simmons, but he didn't return phone calls or messages.

Fear and depression have paralyzed Simmons and made him a recluse, a sharp change from the outgoing and seemingly effervescent personality who has been in the public eye for decades.

The 66-year-old fitness guru has been well known for quirky exercise videos and TV appearances through the years. He has put together 65 fitness videos and published nine books while helping "millions of overweight men and women lose more than three million pounds," according to his website.

Tagsrichard simmons, fitness, depresion, TMZ, celebrities, mental illness, exercise, TMZ