Still have not read the entire thread yet.
But you should not declare.
Can you trust your boss? If yes, let him know and tell him that if possible to cut down your work load and at the same time you look for a new job. If after a few months still cannot work out then maybe lower pay and less responsibilities etc.

It's not time to climb up the ladder at your age and condition. Just look for a much easier job near your house if possible. Of course dun declare your heart condition because no company will ever want someone to die while that person is under them.

Funny though.
Never heard about ppl dying from badminton until recently.