Minecraft started running slowly all of the sudden!

I used to run my minecraft at 60-80fps all the time. But starting yesterday im only getting around 12. I thought it might have been a fluke or something so i restarted my computer and such but still nothing. I woke up this morning to test it out and my cpu usage is back down to normal (yesterday it was running at 90-100% at all times) now its at 30 with minecraft open so i know its not that anymore. Any Ideas?