Your body is obviously telling you that you're overdoing things.
All the symptoms you are talking about, the headaches, ringing in ears, nausea etc are all indicative of a concussion.
You really need to be resting in bed and not doing much of anything.....just because something wasn't seen on your MRI or CAT scan doesn't mean you don't have a concussion.
The MRI and CAT scan were done to check for bleeding but the bruising your brain sustained is still quite dangerous and needs to be taken care of.
I really would advise you to call the neurologist.....you probably did forget what he said and in your initial post you did say that they kept on saying that you had a nasty concussion so you shouldn't dismiss that you didn't.
PLEASE get in bed and don't be doing anything until you speak to a doctor......if you are still dizzy, off balance and falling down it probably means you do have a concussion that needs to be taken care of.
You certainly don't want to be back in the hospital again so PLEASE take it easy.