What can this be? Neck pain after injury, headaches, loss of balance and left sided weakness?

My 12 yr old son fell asleep at school with his neck extended completely back, his father tried to pop his neck when he came home stating it was stiff and he could not move it from side to side. The next morning he woke up and everytime he stands he has a horrible headache, loss of balance, and blurry vision. We ended up taking him to the hospital where he was admitted but they could not find anything wrong so they sent us home after doing a CT that came back normal. Now he is still have the headaches just not as bad, this is going on for 4 days now, but he is walking sideways, towards his left side and has a limp. The primary doctor finally ordered a MRI of the cervical spine today but she only put on the order to rule out herniated disc which I was told would not show if there were any kinds of leaking from a tear etc. I am so confused as to what to do next, my son is not getting better but everyone tells me that he is fine and nothing is wrong?

[Londres70]

Well, everything doesn't sound "fine."  Sounds like it is coming from his cervical spine or the back of head.  A MRI of the cervical spine will view the back of head as well.  I think his dad misaligned something when he was trying to "pop" your son's neck, which I would never recommend anyone doing.

I would request a referral to a Neurologist as well.