Panacur is top stuff, he should be OK with that.
If the wind stops all well and good but if not he may need a stool sample analysis for bacteria.
I have this sporadically with my two older females, intestinal bacterial infection can be shared by litter tray use and both my ladies use the same tray, so both get the same tummy bugs. My vet, thankfully, takes a pragmatic approach in that a Covenia anti-biotic jab has sorted out the bacterial infections previously so we don't bother putting the old girls through the rigours of blood tests (as the cure would generally be the same anyway) but this is NOT doing it by the book, so you would naturally expect the vet to request stool samples and bloods.
I've also been sneaky in former, leaner days by dosing left over Synulox tabs (from one of my other cats), which worked a treat but obviously that's so far out of order I'll likely get told off by the mods for mentioning it