What Causes Extreme Fatigue And Disorientation Post Brain Surgery For Lesions?

I had brain surgery three years ago. I had brain lesions, but really never got a real diagnosis. They said that it was inflammation. I had a pulmonary embolism 2 weeks after surgery. I now experience extreme fatique, very sensitite to heat and tire very easy. I have episodes where I feel disoriented, drunk and my mind seems cloudy. My body slows down, I walk slow and this use tolast for one day then the next episode 2 days now it's lasting 3 to 4 days. When I take a prednisone, the next day I feel normal. I have generalized weakness and I don't know what's wrong. I forget a lot, I am not the same person.