Hi
Welcome to the MedHelp forum!
With a history of headache, dizziness and sleepiness after head injury, it is important to get it evaluated ASAP. Hence go to an ER and get the requisite tests which will also include a brain CT scan or MRI. The symptoms could just be the jarring effect of head injury. However it could get serious too. Hence an evaluation is a must, especially since you are feeling sleepy.
Hope this helps. Take care!