How exactly are those of you calling each other "idiots" and "disgusting" helping the OP? Stop making it about yourselves.
The fact is, the dog needs to see a vet, the OP is aware (by the obvious guilt) that they need to apologise to their mum and knows what they did was wrong, and the brother needs help (both in terms from a doctor in regards to medication if they're not already on it - or a review if it's not working - and the family sound like they could use some support generally, whether that's from social care or a voluntary service).
OP, if your dog hasn't improved, go to the vet. If your mum isn't back yet, just leave her a note for now - tell her you're sorry, where you've gone, and that you really want to talk to her when you get back. Call her or send her a text on the way to the vet if you prefer, at least until you can speak in person.
The rest of you need to calm down, get off your little soap boxes, and stop being so dramatic.