My three year old male German Shepherd was outside in the backyard with my 4 yr old female Pitbull. I heard a loud bang and looked out the window. I opened the door to let them in and my Shepherd couldn't make it up the stairs. He kept falling down like something was wrong with his back legs.
He wasn't fainting or having a seizure. It appeared that he was posssibly dizzy or like something was wrong with his hind legs. I got him in the house and he was panting heavily, bleeding from his back legs (from falling), wagging his tail rapidly,. I tried to give him ice, but he refused. He drank water. I walked with him to next room to see if he was limping, but he wasn't. As I was checking him, he urinated or sprayed a little bit which is odd behavior since he uses the bathroom outside. I got him to lay down to continue checking him for injuries, but it was making him more nervous so I stopped to let him calm down.

I went in the yard to see if I could piece together what happened outside and I saw that he threw up his diner.

When I went back inside he was panting and his breathing slowed down. He is acting normal now. I'm going to bring him to the vet tomorrow, but it's 11 PM. Can anyone help me figure out what is wrong with him? Thank You

At best, it's a mystery. I wish I could tell you. Rough play that went awry? Syncopal episode?
Is there an after hours vet that you could call in your area to run this by?

Do you know what the loud bang was? Maybe he got startled and in reactiont hrew up? It would really be just a guessing game at this point, but please keep us posted as to what happened.