Why is my minecraft running slowly out of nowhere?

One day my minecraft was running just fine and I was getting around 60 fps, The next day the fps dropped to around 30-40 fps. I have now idea why, I just reinstalled windows a few weeks ago and there are no other intense programs running while I play minecraft.

Open Minecraft, go to your video settings, and make the max framerate to 30. It will improve your gameplay.

Suggest you that You need 15% or more free HDD space to defragment effectively. And also
Do these issues happen on AC power, or battery, or both? If only on battery it could be that fluctuating power

Download Optifine, turn down your Video Settings, or get a NEW computer. Make sure you arent running any other apps also