Hi Sir or Madam,
What is his temperature?
By breathing fast, is he panting?
What type of abnormal behavior are you seeing?
When did he last eat?
When did he last drink?
Are his gums moist or tacky?
Was he outside in the heat for an extended period of time?
Are his gums nice and pink or paler than normal (white or gray)
Dogs have a normal temperature of 101-102.5F, so to our hand, they always feel very hot. the only way to know for sure if he has a temperature will be to take it rectally. A normal thermometer can be used. . If using a digital thermometer wait until it beeps to read it, otherwise leave it for a full minute before reading. A dog's temperature is 101-102.5F.
If your dog's temperature is over 103F, you can use a damp cool towel or ice packs on your dog's abdomen and feet to try and cool your dog down. You can also use alcohol on the pads of you dog's feet. Offer cool water (not cold).
If it is over 104F, don't wait, take your dog to the nearest emergency Vet.
Many different things can cause constant panting. Heavy panting can be caused by heart problems, lung problems, fever, or bronchitis. You can read about this here:
Dogs pant for various reasons. They pant to cool down, but they also pant when they are under stress, in pain, or afraid. There can also be medical causes such as neurological problems, respiratory disorders, and Heart problems such as heartworm, anemia, and fever.
If your dog is panting but has no other symptoms (doesn't have a fever), keep a watch on him. If it still seems excessive after a day or so, or if he develops more symptoms, I'd schedule an appointment with your Vet.
Since he just ate at noon, we really can't say he isn't eating yet. He could just have an upset stomach or have some discomfort from an injury. At this point it would be hard to say without an exam. You can give your dog some pepcid or Zantac to help with an upset stomach if you feel that is the problem. Read about Pepcid dosages and usage information here:
Zantac can be given to a dog at .25 to 1mg per pound every 8-12 hours. Read about usage here:
If an injury is possible, Buffered aspirin can be given to a dog with a dosage of up to 5-10 mg per pound every 12 hours until you can get him seen. Keep in mind that a dog's body does not metabolize aspirin in the same way as a human and thus should not be given more than a day or two without contacting your Vet. Read side effects and precautions here.
I'm also going to give you information on heat stroke so you have it. Symptoms leading up to heat stroke include heavy panting, deep breathing, excessive drooling, then dry gums as your dog becomes dehydrated. You will also see weakness, confusion, inattention, vomiting and diarrhea and sometimes even bleeding. The gums may also go gray or very pale as well and will progress to seizures and or coma if no treatment is started. If your dog's temperature reaches 105F, then it is very dangerous and your dog needs to be seen immediately.
The best thing is to try and prevent it by allowing your dog to slowly work up to exercising on hot days, make sure there is plenty of water and the dog has access to it and if you see signs of overheating, then move the dog to an air conditioned area for recovery. Most dogs I've seen with heat stoke have been ones that were trapped in hot cars, or left with no water or shade in a concrete kennel situation
If your dog is showing signs of heat stoke, you should take your dogs temperature rectally. If using a digital thermometer wait until it beeps to read it, otherwise leave it for a full minute before reading. A dog's temperature is 101-102.5F.
If it is over 104F, start cool down procedures and take your dog to the nearest emergency Vet.
Here is a great site on heat stroke overheating
Hope this information is helpful to you.