My dog went out for a potty break before bedtime. When she same back to the door her head was drooping and she was dripping blood from her nose. She had blood on her front paws and the last 4 inches or so of her tail. I've looked at her feet, I see no wounds. She was shivering when she came in. I've covered her with blankets. Her pulse and respiration seem normal to her resting rate, I have no clue as to what happened to her. I don't feel any broken bones. She doesn't respond to as if she's in pain.. any ideas?

Do you have any plants in your yard that could have done cdamage like blackberries or roses?
Any chance an animal may have bitten her?

It could be a tiny cut somewhere and just a lot of blood.

There is also the possibility that she may have caught a small animal and "satisfied her hunger".

Do you live in an area with snakes or spiders that could cause this kind of damage? Any signs of a cat near by?

By now I'm sure you have cleaned her up. Did you see any abrasions or wounds? Look everywhere especially around her head and even in her mouth. Is she in a fenced area when she goes out? Seen any strange cats or dogs? Blood dripping from her nose and on her front feet seems to suggest that the blood may be hers, from a nose bleed or a laceration in her mouth, but that wouldn't explain the blood on her tail unless she were slinging it or chewed on her tail. Many possibilities, I do hope you report back to us with an update.

This is scary, because she can't tell you what happened.

If she seems stressed, and obviously there's blood, then a trip to the vet is the only thing I can recommend.

We really don't know what happened any more than you do. Your vet will at least be able to tell you if she's okay.