The Black Sabbath singer was diagnosed with the progressive neurological condition in 2019 and had been experiencing constant pain for the past year.
Parkinson's disease, which currently has no cure, is caused by the death of dopamine-producing nerve cells, leading to three main symptoms which include tremor, slowness of movement, and rigidity.
Some subtle symptoms may include a change in a person’s walking pattern, very small handwriting, a loss in their sense of smell, nerve pain or insomnia.
Symptoms, which can develop slowly over several years, usually occur when the brain is no longer able to make enough dopamine to adequately control movement.