When your dog might be experiencing internal bleeding your dog should have a rapid heart beat and shallow breathing, Black Diarrhea, changes in the color of your dogs gums such as going pale or blue.'
If your dogs gums turn pale or blue then it's a very serious indicator of internal bleeding of your dog.
Other symptoms of internal bleeding in a dog are whimpering when touched, Glazed eyes and inability to focus.
If you notice any of those symptoms then your dog is most likely bleeding internally and you should get the dog to the vet asap.