My cat's been acting strangely for a few days

Hi everyone, as the title says, my cat Milo has been acting a bit strangely lately. He vomited some clear, see-through liquid two days ago, and since then he hasn't been eating as quickly or with as much enthusiasm (he's usually a real glutton). He's also hiding more than usual—he’s been sleeping under the bed and isn't being as cuddly as he used to be. Other than that, he's behaving fairly normally, although he's definitely lost his usual spark. I'm really worried about him.

Thanks in advance for your help, I'll be reading all your replies!