Hello, Thanks for the query.
Your's son hurts his head and in the back.
Since he is feeling somewhat nausea, dizziness
All these things are related to head injury
that too in the back of head.
Presumed that injury is not serious that's why there is simple vertigo
to your's son.
Here one thing is to be noted that every injury to the head that too in medullary region ( back) should be taken as serious , so please get MRI of that part after consultation of some doctor.
If injury is minor as just due to fall than do two things.
1 complete bed rest
for three days.
2. Treatment for vertigo after the advice of doctor.
Have a good luck Dr. HET