Why is my hubby trembling/shaking...?

I don't know why but all night my hubby has been trembling and just shaking i keep asking if he is alright and he just tells me he is cold but then he starts sweating when he gets under the blankets. He is recovering from pancreatic cancer surgery and is expected to make a full recovery. He has been doing so much better lately just has me worried don't understand whats going on with him i told him i want him to go see his doctor in the morning but he just told me no that he is tired of doctors. What could be causing this? Advice?