I am a 76 yr old male. in last 2 weeks I have begun to feel somewhat dizzy when standing up, walking around corners, climbing steps. Loss of energy, simple chores are kinda exhaustive. Also, severe nite sweats and occasionally shivering chills even with bedding pulled up. My stomach seems to be enlarged somewhat and filled with gas. My weight is normal for my height. I have not noticed these symtoms in the past. What may be wrong??