I went and saw the doctor again. All the tests came back negative, which means if there is something wrong with me, they don't have any idea what it is. One one hand that is great, on the other hand it still leaves the question why I fell and knocked my head.
No one at work wants to say it was a slip and fall due to workman's comp issues. Only one person was around when it happened and his statement isn't very helpful. So it looks like the question as to what really happened will go unanswered, unless I have another incident.