Where did you hit :at home or outside ? How was the surface?
Was there any loss of consciousness
following the event?
See in your case because you were under the influence of alcohol so I presume you would not remember the post impact events. Hence it becomes little messed up.
Anyways because you are having drowsiness, double vision
and nausea it can be both because of hangover as well as head injury
. Also as back of your neck hurts and you are not able to swallow so maybe you had hit the cervical spine
area along with he back of the head.
Whatever rather then predicting, I would suggest you get the following investigation done:
CT scan Brain and cervical spine ( without contrast)
See a Emergency physician with the report.
If the report shows normal then you may need an analgesic anti inflammatory tablet for about 5 days and a soft cervical collar