Tailbone is the pointy bone seen at the lower end of the vertebrae, which is also called coccyx. If there happens to be a bruise or a fracture in this tailbone, even sitting down simply can cause hectic pain, which will shoot up your spine.
Although the pain may be harsh and persistent, a majority of the time, you will just have a bruise. You can see swelling or a bruise physically, if it is a bruised tailbone, and this will reduce and cease with time and by treating correctly. On the other hand, there is every possible chance to break or fracture your tailbone, and this is not something unusual. If the pain felt affects your daily activities, it is time for you to visit a doctor and undergo all the tests needed like an X-ray initially to verify whether or not you have bruised or broken/fractured your tailbone.
A visit to the doctor is highly recommended if you have a tailbone injury, because the pain may be due to more serious underlying medical conditions in which case further investigation and various medical tests to be done.