Feeling Thirsty, Weakness, Heart Flutter, Had Bypass Surgery. Am Diabetic. What Is This?

I m not sure what type of doctor did the surgery , but my uncle had bypass surgery because blood wasn t coming to his foot . He is a diabetes patient . The doctor has told him that he has too many fluids in his body so he shouldn t consume a lot of, say, water. But my uncle feels really thirsty. Also, when he s told to get up and try walking around, he says he feels to week and and his heart feels nervous or something like that...like maybe butterflies in your stomach kind of thing but in his heart/ chest area? I m not sure. Can someone please tell me what this is?