[Gameplay] Black screen bug but can still move and hear things

Just played a zilean game, where everything started normally, but then a few minutes in I had a major bug happen. I'm not sure if this was a bug on my end or with the actual game. What happened was, I heard this weird sound and all of a sudden my screen went completely black except for the in-game cursor. I could still hear everything. I tried clicking around, which apparently worked because in the replay I watched, it showed me randomly walking around. My cursor would change to red when I was over an enemy. Then, I died (but it didn't get announced so I didn't know). I kept trying to click and with my screen still locked on the same area, it caused me to walk all the way back to bot lane (I guess I thought I was walking away from the fight, because I had no idea I died). Then I died again, and heard the announcer say it this time. At this point I was trying hard to open the task manager. I got it open, and I was on my desktop, but my desktop was black for some reason except for the bar at the bottom that shows you what you have open. Every time I clicked task manager, it opened League back up. The whole time I was trying to type in the league chat so that my team knew I wasn't trolling, but I had no idea if they could see it. After mercilessly trying everything I could think of, I finally decided to force restart my computer. I loaded up the league client and got back into game and explained to my team what happened. They (for good reason) thought I was a troll until I explained, but they were very understanding, and we ended up winning. Also, they told me they couldn't see anything I was typing.
I'm scared this will happen in another game. Can anyone explain what this was?