Casualty star Derek Thompson feared that he had Parkinson's disease when he started suffering from strange symptoms.
The actor - who bows out as nurse Charlie Fairhead after 20 years in tonight's episode - felt terrified when he started having cramp in his neck, as well as twitches and tremors of his head.
Derek hid his symptoms from his cast members for six months but eventually decided to see a doctor. He then discovered that he was suffering from dystonia; a neurological disorder which causes involuntary muscle movements.
"I went to see a specialist, a neurologist, who was about 7ft tall, very expensively dressed and was very upper class," Derek told The Mirror.
"He said, 'Have you ever heard of dystonia? Well you've got it. You were worried it was Parkinson's weren't you? It's a life sentence not a death sentence. You will have it for the rest of your life'.
"But I thought this is a relief because he was right, I thought it was the early onset of Parkinson's."
Thompson then contacted the Dystonia Society and was advised that botox treatment would reduce the severity of his symptoms.
"I had botox treatment and the transformation was instant," he said. "Within a week the symptoms had dropped to about 10 per cent of what they were previously. It was extraordinary."