Thank you for your query.
You mentioned that your son said that he was unable to see. Thereafter what is the situation. Is he able to see now or still not able to make out light or people. In case he is able to see then you can wait and watch. However, if he is still unable to see then it needs to be taken seriously and he be examined by the doctor.
some do get black outs and may complain a transient loss of vision. This becomes normal in a short while.
I hope I have answered your query to your satisfaction.
Wishing your son an early recovery.