Full screen
 

When I am in fullscreen, and randomly click a mob or just somewhere on the screen, it closes back out to windowed mode.

Any help is appreciated.

Sounds like you have dual monitors. I downloaded an app to clamp mouse to one screen then use a hotkey to togglr this on/off.

Go into your eqclient.ini file and set the windows and fullscreen resolution to match the resolution you are using on your monitor.