Okay, at the bottom of the editor, there should be a set of four buttons on the left side. The right-most button looks like two arrows pointing in opposing directions. Is this button blue by any chance? If it is, click it once to turn it off (it should be gray now). If that was the problem, you should be all set.
It is a special mode for people that like their screen to split off and act like a three-pane viewer.
P.S. As long as you start breathing again as soon as you’ve demonstrated your chromatic versatility! It occurs to me that you may misinterpret my last message as some sort of malevolent murder by proxy - not at all the intention. But I ask you, is it fair to wind up a hard-working developer who hasn’t slept for weeks???