Given the symptoms and the conditions under which they occur, I would strongly suggest you put the squash matches on hold until you've had an opportunity to have yourself evaluated for heart disease, and if that's positive, then have it treated appropriately, so that you can then safely return to doing what you enjoy.
First priority is to protect yourself. If this is due to heart disease (and the symptoms and your age point argue in favor of the possibility) then you'll need to do some things to correct the problem. Since you haven't been felled by a coronary event as yet, you may well be able to dodge the bullet altogether and return to your active lifestyle. However, if you continue to push without checking this out, you may not afford yourself the opportunity to live a long, competitive life on the courts.
I hope you'll stop play long enough to determine what's causing this and follow it up appropriately. Best of luck to you. Please keep us updated.
John Kenyon, EMT, CCT
Non-invasive cardiology tech, Emergency and Critical Care technician, Critical Incident Stress Mgmt. specialist