When I was in my early teens I used to hear people screaming at me(it sounded like my parents..) I even started to think I was crazy.
One day I thought I had completey lost it when I started to see writing on walls everywhere I looked. It looked see-though but I could see it on the walls. Every time I tried to read it It would blur out. I was so freaked about it cause I thought that ever I was crazy or I was being send a message from GOD himself. One day I cried hard because I thought I was a weird. Then the next day it dissapeared. It never came back again. I must also tell you that I had a rock thrown into my eye a few years before so it may had been some blood floating into the eye that looked like writing. Who knows, the specialist said that sometimes crying for a long time can dislodge floaters in the eye...
Anyways I think that your friend should see a doctor and make an appointment to see a specialist.

Im sure he will be ok.