If it were me, as long as he’s eating and behaving somewhat normally I would give it some time. It may well have been a one off.
Cats are very sensitive to smells etc so it could be the melts or they could have exasperated anything going on. Maybe your mum could stop them for a while.
My boy was hit by a car about two months ago and is slowly recovering from so very bad injuries, they can make amazing recoveries in only a few days. Each day he is getting a little bit more like his old self and he’s 13! Even with insurance vet bills are painful, we didn’t have insurance and we’re looking at a £3k bill