Horrid fps drops since about 3 days ago

About 3 days ago I've been getting horrible fps drops but they haven't been going back up to my usual fps, usually unless I'm in wvw i rarely go below 45 fps in most places on the higher settings. Recently my fps has been tanking to about 7 fps and staying there until I close and reopen the game and I'm unsure what could be causing it. I have loads of other games on my computer which don't lose any fps, even new games just released which I can play on max between 80-100 fps. Looking for help.

Played again today and it was fine until about 2/3 hours after playing, stood still in LA chatting as usual and fps drops ffrom 56 to 7 then to 4 then upto 36 and won't climb any higher as if I've been throttled to that. Only happened since the halloween event was removed.