One thing that often happens after an accident is that the people concerned might walk away from it as if nothing has happened and feel themselves quite lucky, but then wake up the next morning stiff as a board and racked with pain. This sort of delayed reaction is not at all uncommon, so if you are involved in an accident you should always try and get as many details as possible before you leave the scene, just in case.
Even afterwards when you do go and see the doctor, there is a possibility that even the doctors will not be able to tell you just how badly you have been injured for quite some time, if ever. Some injuries will of course settle down and cure fairly quickly, but some of them can take a length of time, which is surprising given your initial walk away from the accident uninjured, or so you thought.
Everything might be hunky dory on the outside, but all sorts of strange things can happen inside the human body without you knowing about it, which it's why it is always a good idea to go and get medical advice after an accident, even if you don't think you've been injured. And if you do this, that makes sure that if you make a claim, when the value of your claim is assessed it is assessed on the basis of what the doctors think will happen in the future just as much as on what you think has already happened.