A New York Daily News story published Saturday said Simmons by and large hasn't been heard from in roughly two years.
Several friends told the outlet he'd suddenly and bizarrely cut off communication with them about two years ago. One friend said he suspected Simmons' housekeeper is keeping him captive with the help of black magic.
The friend also recalled a 2013 interview with CNN as Simmons' last media appearance.
"I wish all of your viewers a prosperous and happy and healthy New Year's," Simmons told CNN.
But a representative for Simmons rejected the claims, telling USA Today: "Richard Simmons has been in the public eye for 40 years, and he's opted out. It's his right to do it. That's the God's honest truth."
The rep said Simmons' "mental health is fine." The New York Daily News says Simmons' manager denied the outlet an interview with the 67-year-old fitness icon.