My father has disease of shivering  in any season. It  not only happens in winter,in summer also he faces the same problem.. It doesn't often daily. May be once in two or three month in summer,in winter once in a week or three days it also happens. He has been suffering from this peculiar disease since last 15 years or more.. Some doctor said that it's a gastroenterological problem and he also had some medicines. But nothing happened. Please tell me Sir or Mam what he should do or take as medicine and what is the root cause of this problem.