Took him to the vet yesterday as he kept shaking his head and sure enough, he had one. The vet have him an immobiliser, a new thing which slows the heart and makes them really floppy but is safer than a GA. It took the vet a while to get it out as it was right at the bottom.
Got him home and he was really out of it and you could feel his heart still doing a really slow thud-thud, and he just fell into a really deep sleep (which the vet had told us would happen). Poor boy wee'd himself twice in his sleep and big sis Bella was all worried and upset. Anyway he's as right as rain today, good to have our bouncy boy back!