You barely notice it because it happens so fast, but there's a brief stutter where the console makes that switch (I regret nothing) from one state to another.
None of the buttons work on any of the controllers, pressing the power button in to turn the screen off doesn't work, and the touch screen doesn't respond to your taps.
Not a fun time, especially if you're trying to get in a few minutes of game time on your work break.
It seems like you're stuck here until the Switch figures out how to unstick itself, but there are actually two different ways to deal with a frozen Switch.
No additional steps required, you can return to your regularly scheduled gameplay.
Pressing the power button in once may not do anything when your Switch is frozen, but there's a hardware reboot in that power button that will work no matter what.