Please talk to your vet....he might need some temporary trannies, or maybe be encouraged to use another window to view the world.
Animal behaviourists can be very helpful too - please look into that.
Worst case - maybe rehome him to a friend who has a 2nd floor apt or something. Please keep us posted!
"I have six locks on my door all in a row. When I go out, I lock every other one. I figure no matter how long somebody stands there picking the locks, they are always locking three." -- Elayne Boosler