Weird FPS Drop

Experiencing a strange FPS drop lately. I sit at a constant 60fps and have never had fps drops before until now. Whenever I do something more demanding such as a team fight it goes from 60 straight to 30 and stays there. As soon as this happens I alt+tab out and then back in and it instantly goes back to 60 and stays there until the next demanding situation. The weird part is that it never goes anywhere in between just 60 straight to 30 then back to 60 over and over. Any help would be appreciated, getting tired of alt+tabbing in team fights.