From what I know wobbly hedgehog stardomstarts with a back leg stop working slowly and then slowly goes over the whole body which will eventually affect activity and weight but, you would know if he isnt using the leg. Also there are loads of other things that come on faster that cause them to be wobbly and not use one or more.
Anyway the eating less could be anything from the hot weather to being ill.
However I wouldn't count a 8g drop in a week a big weight drop. Anything over 20g would be a big drop. But not 8g.
If its just the weight your concerned on keep an eye on it like you are but if nothing else wrong and out of the ordinary then he is likely fine. Take him to the vet if you want to be sure.
Unless he is slowly stopping using a back leg its not worth worrying about whs.