My 82 Yr. Old Husband Has Always Been Healthy With

My 82 yr. old husband has always been healthy with a healthy appetite. He works out for an hour each morning. He suddenly has stopped eating and exercising claiming he has a full feeling and isn't hungry. Is currently on a soft food diet. His personality has changed. He can't sit still, his posture and balance are suddenly stooped and slow. Any idea what's happening? His anxiety level is through the roof.