Abrupt behaviour change (Cat)

[real4star]

Neutered ginger 5yo tom cat with a heart murmur.

Usually found asleep, quiet, lazy animal, friendly, curls up with the dogs, on the nearest lap or recently vacated warm seat... etc etc

Then day before yesterday for no apparent reason he's started yowling as loud as he can and running round the house like he's on fire. Knocking over chairs, mugs, vases, fighting with the dogs and for some strange reason chewing on plastic bags then he calms down and goes back to sleeping. Few hours pass then he wakes up and takes off again.

We haven't changed his diet or the natural rhythm in the house, the vet doesn't have any idea (we checked his teeth incase that explained the chewing/yowling they're fine) he's eating normally.
He doesn't go out (purely house cat) so he isn't being fed/poisoned out doors

Any ideas what it could be?

[bexVN]

Difficult one this. Very random behaviour.

Keep a close eye on his daily routine, there may be changes you hadn't really noticed before. It may be a random one off incident but it is quite a reaction not to have something underlying it. Obviously the vet didn't see anything of concern on examination. However if it continues I would be wanting a more detailed examination of eyes and heart and/or checking behaviour isn't any way linked to a brain problem (to be thorough).

Hopefully it won't happen again and it will forever remain a bit of a mystery.