First thing check:  make sure the GPU card and video cables are firmly connected inside the system.  The drop may have jarred something loose.

17 R4 Service Manual

Try running the ePSA diagnostic. Press F12 while booting and select the diagnostic. It will test all the hardware to see if there is an issue. It doesn't always pick up the problem but it could help. 

I would suggest you to run the LCD Diagnostics on your laptop.

To run the Built-In Self-Test perform the following:
Turn the computer off.
Press and hold the D key while pressing the power button. This will start the BIST.
The screen will display multiple flashing colors. Look for lines, distortion, flickering or any other video issues you have observed.
The laptop will restart when the test is finished.

Also, connect an external monitor to your laptop and check if the external display also flickers.

Let me know the results after performing the above mentioned troubleshooting steps, I would be happy to help you further.

Also if you explain whether it landed on the screen or the laptop body then that would be extremely helpful.