Yep, sorry for not responding immediately when I worked it out. Completely turning off my Discord overlay fixed the problem (but turning it off specifically for Minecraft didn’t fix it for some reason). Right now it seems unclear what the problem cause is, as multiple different things can fix it. I usually use my overlay when playing Minecraft and other games so it would be preferable to have it on. Perhaps on the release of Optifine for 1.14, the problems will all go away. Thanks for your help.
Edit: Added a little more detail.
The first thing I tried was closing my Discord before opening the game. This fixed the issue immediately. Obviously, I'd like to have both applications open at once, though. I recently reinstalled my game (in order to see if that would fix the issue) and found that I experienced the same issue in 1.13.2 until I installed Optifine, which somehow fixed the problem. I have provided my (basic) computer specs for reference.
Processor: Intel Core i7-8550U CPU @ 1.99 GHz
RAM: 16GB
Graphics Card: NVIDIA GeForce MX150
Edit: Removed me being an idiot and forgetting the NVIDIA Control Panel existed and how to get there.
Unsure if commenting here now is okay or not. This is the only instance of this issue that I could find. I'm currently experiencing exactly this in the 1.14 version of the game. Apologies if commenting here is not okay, this is my first time on the bugs.mojang website.
Problem resolved. I'm using Discord Canary (like a Beta version of Discord) so it was just a little glitch. I restarted my computer and just turning off Discord Overlay for Minecraft worked. No need to submit a report to Discord. Glad I could fix this issue. Insanely annoying.