Hi S,
Flat or inverted T waves can be an indication of a lack of oxygen to the heart muscle.
(Un)fortunately ECGs are not the most refined way of finding out what is exactly going on and a fair few findings on routine ECGs turn out to be nowt to be worried about. However the process to determine that there is indeed nowt wrong can be a bit protracted and long winded.
Am sure that your AME will advice you on how to proceed and get sorted.
FD