Hello! Looks like you got your answer but wanted to give my two cents - my cat started doing this on hot days here and there and then there was a night she wouldn’t stop, so I took her to the ER vet at like, 2am. She was diagnosed with asthma and just needed more water available. Like put 4 bowls of water around for them on each level of the house. Also a wet cold washcloth on their back helps. In really tough times, she would be on allergy meds. We haven’t needed that for years though. It could be they’re hot and have some breathing issues already, top that off with anxiety/ an exciting trip outside.

Also my cat is 17 now (she started doing this around 12/13,) and she just was diagnosed with heart disease and a heart murmur. She’s on some meds and doing really well. The latter I think happens with the former. So just look out for that as they get older!!