Sorry I didnt realise the time with you It may be his heart if he has a fluid build up we lost our old tom cat a couple of years ago he woke us in the night crying, dragging his back end round as his bag legs were paralised & gasping for breath we were at the vets at 2am the vet said the gasping was because of a build up of fluid so he pts he was 15 yrs old & hadnt shown any signs at all of illness the vet thought possible HCM but couldnt be sure without a pm & we didnt want that done.

I hope your cat is ok just do what you can till you can speak to the vet x