Probably gonna get caned for this.
But I tend to find that if you have had your computer for multiple years and haven't done a fresh windows install recently chances are that you have alot of shit using up CPU usage, RAM usage or even GPU usage, this can be done by downloading stuff you shouldnt really download, dodgy programs, torrents etc. They soon build up and begin to have a effect on your computer, you know your computer performance more then any of us, I myself when I notice dips in performance I begin with drivers,and the basic stuff such as a general PC clean up.
Had the same issue myself with BF4 one min I could play it fine on my 970, next time it took a dump, a PC clean up or fresh install usually does the trick, of-course if you don't want to format your shit, just make sure you get programs like ccleaner, defrag your hard-drive, check latest drivers etc.