This sounds like your pet may have some sort of pain occurring.
Panting and fatigue may indicate pain, organ problems, difficulty breathing or heart problems, or endocrine disorders. In most cases for his age, this indicates pain ---most likely from pain of some sort.
An examination by your regular veterinarian will probably help to determine the cause. If pain is the cause, more information follows. For other diseases, bloodwork or urine samples may be needed.
The pain may have him "distracted" from his surrounding environment and may make him act ill. Other possible causes could be exposure to chemicals/toxins/medications (may cause many nervous system signs) and also could be due to overheating and gastrointestinal problems - usually these are accompanied by vomiting and diarrhea. More than likely, he has "pulled a muscle" of some sort. Some breeds are known to develop nerve or "disk problems" in their neck, which may cause them not to eat or drink. Other breeds are more prone to back or leg disk or pain issues. Sometimes elevating the food and water bowls to head level may help. This can also be a sign of general problems in the body, and may require an examination and bloodwork to diagnose.
It is possible in pets for strains and sprains to occur, and the most common areas are in the neck and Back. Some may result in severe pain. Sometimes spinal cord injuries can occur, often due to a "slipped disk." The more severe the pain is, the more likely that the injury is serious. This often follows vigorous exercise, about 12 hours later, or sometimes can occur by twisting or turning 'the wrong way.' The panting and rapid breathing may be associated with pain, and may indicate that the pain is severe. Sometimes there can be problems with the disks in the neck - this is an emergency. If your pet has difficulty walking or cannot seem to feel where his feet are, take her to an emergency veterinarian immediately for pain medications, x-rays, and possible injections.
We all know how bad back and neck pain can hurt, so having your regular Veterinarian administer pain medications and muscle relaxers is advised....ESPECIALLY if it gets worse. Rest is also advised. The less your pet moves, the better and faster they will heal. Please do not give over the counter pain medications such as aspirin or Tylenol - these can be toxic and will severely limit the medications which a veterinarian may need to use on a future visit to help your pet.
Most starting medications are Rimadyl, Tramadol, and Methocarbamol if pain is the main cause of signs.
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