Well, here I am, since reddit produced two upvotes and zero comments. This will basically be a copy/paste from there to here.
Ever since I got my new computer(not something amazing but undoubtedly better than what I had before), and one of the main benefits I've had was actually being able to play Minecraft above 35-45 fps, even with Optifine. Now, I'm still using it on this computer, and normally able to consistently have 90-120 at my desired settings; 8-10 render distance, minimal particles as they tend to be an eyesore imo, basically what you'd equate to "medium" settings, I guess. This past week, however, I've been trying to play on a realm that my friends set up, and I've been completely unable to do so. I'll sit at the usual 100-ish fps for a few seconds, then it drops to 0 for maybe 10 seconds at a time. This happens consistently, across versions, on servers, realms, and on singleplayer. I've seen a lot of 1.13 specific issues related to fps when looking online for a solution, but none seem to match this one. I've also noticed that if I run Minecraft alongside the task manager, it uses about 1k MB of memory when not in a world, and double that if in a world. Not an issue given the ram I allocate, I think. What does seem concerning is that when I load in a world, my cpu usage skyrockets whenever I move, and the game freezes when it reaches 100% usage. Then it drops again, but the game stays frozen for a few seconds after the cpu usage drops to about 20%. I've uninstalled and reinstalled the game, updated and even reinstalled java, all to no avail. Anyone able to help me out?
I have an Intel core i5- 2400 @3.1GHz, I usually play at 1680x1050, but reducing all the way down to 854x480 doesn't help at all either, I've only got integrated graphics from Intel, and I allocate 5G of ram to the game.
Well, considering I've only recently started having problems with the game, and both this(and the laptop I had before this one) has integrated graphics, I'm inclined to believe that's not the issue. I'll check out changing how much ram I allocate, though.