[header] How to prevent feline high rise syndrome [title] Secure your windows. [step] If you frequently open your windows, install window screens. These should fit snugly over the window, so there are no gaps. 
Screens allow you to keep the windows open, but prevent your cat from falling out of the windows. [substeps] If you rent your home and can't install screens, consider purchasing an adjustable screen insert that will fit into the open window.