"It has taken me some time to understand the diagnosis, to adjust to it and to decide how much I wanted to talk about it publicly," the singer writes in a statement published by People.
Parkinson's disease is different for everyone, and it can be unpredictable, she emphasizes.
"Some days I'm so tired that I can't get the day started at all. Other days it gives me a little more space to move, think, work and feel like myself," she writes further.
Simon, 83, has stayed out of the spotlight in recent years, but despite her health problems, she has neither "stopped living nor stopped working."
On August 14, the singer's new album "Comes in Waves" will be released, her first full-length album since 2008.
