Mac Sudden Framerate Drop During Game

This has happened to me a couple of times before and it is really annoying considering the only way I can get my frame rate back up to 60 from 5 is to disconnect and reconnect to the game. I only play on Mac and I use the new client on low spec mode. I don't know what causes the issue only that in the middle of the game, my framerate sometimes drops to 5 or lower and it won't come back up from alt+tabbing or anything except quitting and rejoining. It's not game-breaking but it certainly is annoying.