I Am An 82 Year Old Female In Very Good

I am an 82 year old female in very good health. Lately, I have no energy and can just lie down and go to sleep too easily. Due to a rapid heavy heartbeat recently, my cardiologists ordered a a stress test and echo. Got through the walk well and the report proved that all is well. I do eat well, cook much more often than eating out. I do exercise at the YMCA a couple of times a week for about an hour. Any suggestions.