What to do if we have prolonged headache after hitting our head?

What to do if we have prolonged headache after hitting our head?
My friend hit her head on a tree forcefully. It swells on that area and she had a headache. After 2 days swelling is gone but she had headache. Since the day she hit she is having the headache. Now it’s more than a month and even now she had the headache. What should she do? Is it critical?
Will it be dangerous?

There are losts of good answers, but the best answer:

Answer by MP_doc
She ought to go to the doctor… it sounds like she may have suffered a concussion. It’s really best to get it checked out, as it can lead to other problems down the road if not treated.

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