I apologize if I misread your post, ScarletDragon.
I thought you'd already successfully reverted to Windows 8.1, and this loop was something that started happening more recently, after a Windows update.
As Draclvr said, there's a specific way you're supposed to revert to your previous version of Windows from Windows 10. You don't use System Restore to do it.http://www.howtogeek.com/220723/how-to-uninstall-windows-10-and-downgrade-to-windows-7-or-8.1/
To access this, open the Start menu and select Settings. Click the “Update & security” icon and select “Recovery.”
You should see a “Go back to Windows 7” or “Go back to Windows 8.1” option...
I'm not sure what using System Restore would do if you tried to use it to go back to a previous version of Windows. I'd be surprised if Microsoft would even show older restore points after changing OS, but there are a lot of things they haven't thought through lately.
Assuming you still have Windows 10 and it's trying to go to a Windows 8.1 restore point, maybe there's a way to undo going back to the restore point from Safe Mode. If that got you back to a functional Windows 10, you could try to revert to Windows 8.1 through "Update & Security" the way HowToGeek describes.
If your laptop uses the F8 key to go to Safe Mode, try holding it down continuously (or tapping it continuously) all the while it's rebooting.