In case its stiffness and pain in the neck, take rest in flat supine position without pillow. You might require a soft cervical collar
if pain is severe and persistent. Avoid movements at the neck region.
You might need to do : X-Ray cervical spine
(AP and lateral).
If headache is severe and associated with episodes of giddiness then you need evaluation. But what I suggest is that you take rest and see if sleepiness , light headedness and headache subsides. If its still persistent then get a CT Scan brain (plain) done to rule out any head injury
Also watch out for any drowsiness
, vomiting, fits, blurring of vision, severe headache
as it might indicate an underlying head injury.