If you wear glasses, do not go back to your optician to have them changed until you have fully recovered from your concussion. Not everyone has headaches after being knocked out. When they do happen they can have many different causes. Two common ones are fatigue and stress. Fatigue headaches are signals that you need to sleep and doing just that will get rid of the headache.
Stress headaches are also signals.
Again, sleep should relieve the headache, or you may only need to stop what you are doing and change to something more relaxing. If the headache gets worse and cannot be relieved, see your doctor. Occasionally, people find that they get a giddy feeling if they move or change their position quickly. Usually it is only a problem for a day or two. If you find that things seem to spin around if you sit up suddenly after lying down, or if you turn your head sharply, the only way to cope to avoid such sudden movements or changes in position until it clears.