I'm a teacher.yesterday,i was sitting.1 student walked by me &accidentally hit my head's back(left side)with her elbow.my head's back hurt&i instantly felt nauseous.still feel nauseous&the pain where the head was hit.is it concussion?how to treat it?

Summary: from minor trauma as you describe, concussion is unlikely but not impossible. sx may include headache,nausea,difficulty concentrating,mild memory loss. to recover stay hydrated, rest in dark quiet room, avoid screens, tvs, phones, etc. Try not to overexert yourself, do not focus on things for a day or two i.e reading or focusing on small print will make things worse. Tylenol for headache

Head Injury: It is apparent you sustained a head injury and might have had a mild concussion without loss of consciousness.Most injuries like this do not need any treatment and one feels normal after few hours.But if the headache and nausea/vomiting persist you should go to ER and get it checked and may need a Cat Scan to rule out Subdural Hematoma