Hello there jams
This sounds very strange and in my opinion it would be best to take your son to the doctor. It can’t harm if you check if everything is fine with his eye sight and there is no need to risk. Considering your opinion that in question is ocular migraine it is possible.
But ocular migraine is painless and temporary visual disturbances that can affect one or both eyes.
This can be frightening especially when it is happening to 11 year old child. But the good thing is that ocular migraines are harmless and self-resolve without medication within 20 to 30 minutes so giving Tylenol to your son maybe wasn’t necessary at all.
Anyway after examination you will know for sure what is wrong (if there is anything wrong) and keep us posted.