My dog delirious after running?

I see that you live in Australia. It's possible that he gets over heated, or have too much exercise. Either cut down his exercise, or increase his diet. And regardless of your choice, give him more water. Maybe take little water breaks during walks? If this still continues though, definitely take him to a vet. It might turn out to be a heart or other health problem.

For a dog that is usually active that is suddenly having a problem it is time for a vet evaluation. It sounds like exercise intolerance and could indicate an underlying and undiagnosed heart condition. You are best to stop running him until this is checked. The panting heavily after running also is an indicator that there is a definite problem. Next time you may not be lucky - he may stumble and not get back up.

I am concerned that it's a heart condition. I'd get him to a vet asap.

Take him to the vet that doesn't seem normal.