This output appears to show your computer in Nvidia Performance mode. I would think you the nvidia-prime-applet would be an Nvidia icon in your lower right section of the screen on your panel. Not all manufacturers use the same technology for switching graphics, so that may be why you ended up with the black screen instead of the system just using the Intel graphics.
Graphics:
Device-1: Intel 3rd Gen Core processor Graphics vendor: Lenovo
driver: i915 v: kernel bus ID: 00:02.0
Device-2: NVIDIA GF117M [GeForce 610M/710M/810M/820M / GT
620M/625M/630M/720M]
vendor: Lenovo
driver: nvidia v: 340.108 bus ID: 01:00.0
Display: x11 server: X.Org 1.20.11 driver: modesetting,
nvidia
unloaded: fbdev,nouveau,vesa resolution: 1366x768~60Hz
OpenGL:
renderer: GeForce GT 720M/PCIe/SSE2 v: 4.4.0 NVIDIA 340.108
direct render: Yes
You should be able to switch to using Intel by changing the mode on the nvidia-prime-applet and rebooting the computer. Because your computer reacted a little differently after installing the Nvidia driver, I will not make guarantees that switching will work perfectly.
However, you can take a Timeshift snapshot of your system as it currently is so you can return to this state if something happens. Keep both this snapshot and the other snapshot--just label them in the comments field so you know which is which.
You mentioned earlier about how long it was taking to boot. Forty-five seconds is not a long time for a hard-disk drive running Nvidia graphics. An SSD would probably make your system faster, and possibly using the nouveau driver might as well. I have heard others say using the Nvidia driver meant their system was slower to boot. I believe that may be because of how the Nvidia modules build and load during the boot process.
Please go to your first post in this topic, click the pencil icon, and add [SOLVED] to the title so others know you are no longer seeking help on this Nvidia driver issue.