My cat is really scaring me.
He hasn't eaten any of his dinner, he is batting around any of the toys he usually plays with, he doesn't want to sit on my lap or be petted like usual, he isn't responding to his name, or anything for that matter,he's sleeping in my baby brother's bed instead of his own cat bed all of the sudden, he's walking really slow and keeps slipping on hardwood floors, he isn't protesting to being picked up, and he keeps laying right next to the stove, as close as possible to touching it without actually touching it, on the stone floor surrounding  it, which he would never dare go near before. I keep picking him up and moving him because it isn't good to be that close but he goes right back almost immediately.
It's his birthday this Sunday and I'm just really worried.
He isn't a young cat that's for sure.
Mom insists he just has an upset stomach and  that I should leave him alone but I'm worried
I don't know what I would do if he died, he means so much to me, and I live in this almost constant fear of it and it's going to happen some day
But it would be even worse of it happened now because it's almost his birthday and I'm supposed to leave for Europe in a week so being a sobbing mess won't help anything

Please help me