He could have a pinched nerve, injured his back or there could be a tumor. There are a number of things that could cause this. Take him to the vet, who will be able to diagnose his condition.
Most likely a ruptured disc in the spine. Can be fixed with various medicines, but usually ends up in surgery.
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He probably has some kind of injury to his paw or leg. Have him lie down and thoroughly examine his paws, toes, in between his toes, and his leg and groin for any injury, anything in his fur or skin, area that is sensitive to pain, etc. If you suspect a broken bone or find something serious, see a vet ASAP.
i guess because it can't balance, we walk on two legs because our body's are facing vertical. Dogs body's go horizontal so it needs it has a set of legs at the front and a set at the back, it needs to be on both sets of legs to balance its horizontal position, if it is on its back set of legs then it cant balance the front. And there bones are just not built in the right position
There are a variety of potential causes, ranging from trauma (broken leg, torn muscle or ligament, herniated spinal disc, etc.) to infection (myositis, neuritis, meningitis, etc.) to inflammation (rare reaction to vaccine, auto-immune disease) to cancer (myosarcoma, osteosarcoma, neuroma, etc.).
The most common reason would be an injury or illness; you should take your dog to a veterinarian soon for an examination. Without further information (can't walk vs can't rise vs will walk but not fast or for long, for example) any other answer would be speculation.
I stabbed him with a shapened umbrella, it was accident, there blood all over stool.