Hi I Fell Down The Stairs At Home Saturday Night...

Hi i fell down the stairs at home Saturday night... I fell from the top and seemed to bounce twice then hit the bottom hard... i was still concious but had an instant pain in my lower back above the bum cheek on my left side... i do have some small bruising but no other visable signs. I am however worried i might have done something internal as it hurts to walk sit lie bend and stretch.. please could u advice me on what to do.
Thank you