Have you applied all the windows patches?
Is it possibly only happening when you're typing? Or are you basically mouse only and it happens?
Does it seem to happen only when clicking on a link or something?
The icon Schlep is referring to (Win 7 but not Win 10) is sometimes hard to see. If you hover your mouse pointer or just click in the lower right corner of the screen for a few seconds it should go back to the desktop. But when you move the mouse out of the corner or click the corner again it should bring the browser back up.
Since it just recently started happening do you have any antivirus running on it? If so run a complete scan before you go to bed and let it run all night.