Internal Injuries

• Internal injuries from being hit by a vehicle or blunt object can cause your dog to stumble and fall over. If she is suffering from internal bleeding she may vomit, be excessively thirsty or be bleeding from her ears, mouth, nose or rectum. She may also have a rapid pulse and seem anxiety ridden. If your dog is acting drastically different and falling down, she needs to see a vet immediately.
  
  

Poisoning

• If you suspect your dog has eaten or come in contact with a chemical or poison, this could be the cause of her staggering and falling over. At this point she is suffering internal injuries because her stomach, liver and kidneys are falling prey to the poison. Sometimes, symptoms of poisoning may take a few days to show up and damage may be irreparable. The sooner you get her to a vet, the better, as the vet can give her a laxative to flush out the toxic substance.
  
  

Disease or Condition

• Middle-aged and older dogs sometimes contract vestibular syndrome. Vestibular syndrome causes the nerves that connect the ear to the brain to become inflamed. This can come on quickly and will cause loss of balance in your dog. Stumbling and falling over may also be the result of an ear infection. Your dog also could have suffered a stroke or may have a brain tumor, so she needs medical attention.
  
  

Age

• If your dog has slowly come to the point where she is falling over when she walks, this could be arthritis, hip problems and weakness in the back legs. It is possible that a vet can treat her conditions with drugs, but this may be a permanent sign of aging. Your vet is the only one who can accurately diagnose these problems.