Hello. Thanks for asking from HCM.
I can understand your concern. Headache after injury is normal. It becomes serious if it occurs even after taking medication or increasing in severity. This type of headache suggests serious type of 
head injury. In such case, consult ER as soon as possible. The doctor might advise you 
CT scan of head to rule out 
fracture or intracranial bleed. Further management will be decided after Ct report.
If your headache is mild, not increasing and you are getting relief after taking painkiller, it appears to be mild head injury. You can observe yourself at home. Observe other signs of dangerous head injury 
: vomiting
: loss of consciousness
: decreasing consciousness
: fits
: bleeding through nose/ear/throat
If any of above sign, follow dangerous head injury instructions.
Meanwhile at home, you can
: keep your head higher than chest
: apply icepacks at injury site
: take painkiller like 
Diclofenac sodium after proper prescription
: take rest
Hope it will help you.
Thanks. Take care.