He hasn't eaten since yesterday morning and I don't think he's had a drink that I have noticed. He's heaving terribly...and there's nothing but foam to come up. 
I've called the vet and they say to come in at 6 but I'm terribly worried...what could it be? His eyes look sticky and he's not hiding away but will come and sit on me uninvited and purr when I stroke him but he's turned down water and food (I put some drops on my finger and dabbed it on his tongue a few times today) I'm SO worried.