This is a very serious injury that should be treated immediately by a vet. Your rat may bleed from the nose or ears, fall in and out of consciousness, or even have seizures. Stay calm (for both your sake and the injured rat) and gently place your rat in its comfy travel cage. Have a friend or family member drive you to the vet, while you try to keep the rat as comfortable as possible. Signs of head-tilt may also indicate head injury or brain tumour, if no (inner) ear infection can be detected.
Like previously said, this injury can be serious, and can end in death. Although it may be hard to decide, you might be faced with the decision of euthanizing your little one. Think about the rat before yourself, however heartbreaking it might be. If the vet suggests euthanization, then it’s probably best to do so. Say goodbye to your little friend, and wish him/her luck on their next journey, and remember, they had a wonderful life while they were with you.