If you fell when you were hit, you could have jarred various parts of your body.
And while you may not have lacerated or ruptured you kidney or spleen, you very well could have bruised it. You could have bruised your diaphragm. You could have some costochondritis (inflammation of the costal lining of the ribs).
and it devolves into a vicious circle: because you aren't sleeping your body isn't resting, and isn't getting a chance to heal it's self. Because your body isn't healing you're hurting and your can't sleep....
I say go back to Dr. get a second opinion

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Mental that one, I'm telling you. ---Ron Weasley, "Harry Potter and the Chamber of Secrets"