One of the comments:

It's only being referred to as a mystery illness because the family hasn't found it necessary to tell the public their business. His mother died from a serious autoimmune disorder when he was only a teenager. Then there was the plane crash he survived with 65% body burned, blood clots a couple of times since then. BTW, he's Catholic, goes to church, prays with his children and definitely believes in God (and hasn't made a secret of it.) I'm keeping a good thought for him. He's a fantastic drummer, seems a good father and stepfather and is friends with his ex. It would be awful if something happened to him as his life was just going so well.