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The following are indications that you would need to visit the Emergency room following such an incident:
1. loss of consciousness
2. bleeding that does not stop in a few minutes
3. if you are taking any medications that are considered blood thinners such as a daily aspirin, coumadin, etc.
4. you are confused or those around you think you are confused.
5. you have a loss of memory
6. you have any changes in your vision, hearing, speech, balance.
Now if you feel fine with only a slight headache, do not take aspirin or ibuprofen. Stick to a pain medicine like Tylenol. If you wake up tomorrow and feel worse, you should call your doctor and explain what happened. He/she may just want to see you in their office on Monday.
Please let me know if you need any clarification or have additional questions!