Hi, last night my husband (42 and in good health) woke up in the middle of the night shivering intensely and was freezing. He said his stomach was ok, but he had a headache yesterday afternoon and through the evening. We turned up the heat and after layering a lot of blankets on he managed to warm up but he was shaking very intensely and it was very unusual. Any ideas as to what caused this? This morning he feels lethargic and sore.