I was hoping to get a little more information from you, before sending my answer, but I didn't want you to wait too long for an answer, either.
From your description of his symptoms, it's possible that your cat has an oral/dental problem like an abscessed tooth, infected gums, something stuck between teeth, in the roof of his mouth, between gum and cheek, under his tongue, or something wrapped around his tongue.
Excessive drooling can also indicate nausea. If he's normally, now, his stomach is not empty, but he may have acid reflux or excess stomach acid which causes the nausea. An over the counter acid controller called Pepcid AC or the generic, Famotidine, may help calm the nausea and stop the drooling. You would give him 1/4 of a 10mg. Pepcid AC one half hour before a meal, or you can give it now, to see if it will help. Here is more information:
Another possibility is that he chewed on an electrical wire and burned the inside of his mouth, or licked a caustic or toxic substance.
Older cats can be more prone to develop certain medical conditions like diabetes, hyperthyroidism and kidney disease. Wanting to eat more may indicate diabetes or hyperthyroidism, among other conditions, so a routine senior blood panel, including a thyroid test, would be advisable at this time.
The blood in his drool may indicate either an oral/dental problem or he may be bleeding from his esophagus or stomach, so I would recommend an in-person evaluation by a vet, asap. If your vet is closed now, bring him to the nearest ER vet center.
With his pupils being dilated and you said he seemed scared, something may have frightened him or something is going on in his body, making him feel sick, so seeing the vet tonight will provide you with a diagnosis and treatment, so he's feeling more comfortable.
I hope all will be well with your furry boy and please let me know how he's doing. Thanks!
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