I Am 78, Play Senior Basketball, And Recently Started Feeling

I am 78, play senior basketball, and recently started feeling a burning pain in my esophagus, it goes away after a while on its own but sometimes takes a while, sometimes not. sometimes I get a mild case when I get up from a lying down position. Had a stress test about 2 yrs ago, Dr said I have strong heart, like a 20 yr old, BP is good, pulse is low, what happening?