Re: bad day
The advice to see a vet is good advice. A cat that isn't eating, depending on certain circumstances, can be very serious. If your cat is basically a thin cat, and has little fat to draw from when it's fasting, it actually stands a better chance of survival than a cat with an abundant supply of fat.
What happens with a cat with plenty of fat, is that the fat is moved from it's tissues to the liver. The fat overwhelms the liver, and causes a disease called "hepatic lipidosis". If not treated quickly enough, it's generally fatal.
The primary reason a cat quits eating is due to upper respiratory infection disabling their ability to smell. To a cat, smell is an essential stimulus to their appetite. If they can't smell, they don't eat. What you can do to encourage them to eat is to get the smelliest food you can find, one that they could smell through plugged up nostrils. If they smell it, they'll probably eat it. If they still won't eat, you can smear some of the food on their paw, and they'll lick it off. Even ill, most cats will still try to groom themselves if they get something sticky on their fur.
Incidentally, a cat under stress, which would be one way of describing a cat that has panicked due to fireworks, becomes very susceptible to upper respiratory infection. You hear of cats that quit eating while their owner is on vacation, or experiencing other stressful things, but it's usually because the stress weakens their immune system and they develop a URI. The URI will generally clear up in a few days, but the secondary problems can create the real problems.
Here's a site that offers a fairly good explanation.
