Are you sure you didn't land on your head? Go to the hospital!
When the only tool you have is a hammer, every problem begins to resemble a nail.
Hard to say without examining you (and it would be an unusual injury) but you from what you describe, you may have taken off the tip of your olecranon when you fell on it. Does the 5p piece feel hard (bony)? Do you still have a full range of movement in that elbow?
Best thing would be to get someone to have a look at it +/- X-ray.
Hope that helps
Dr Jeremy Hyams
GMC No. 6052934
Dr Jeremy Hyams (GMC 6052934) - Sport Doctors UK Managing Director