Photoshop :: Panoramic Photomerge Cripples Computer Until Restart

I frequently use Photoshop CC to create panoramic images with Photomerge. I've found that as soon as I start the Photomerge process, my computer becomes absurdly slow. I'm not terribly surprised by this - my primary issue is that the computer remains insanely slow long after I've closed Photoshop CC. The only solution I've found is to restart the computer. Even this can be difficult, because the computer becomes slow enough that it takes minutes to shut down.
 
I want to make a point clear here: I'm not complaining about how my computer becomes slow while using Photomerge. I believe this is to be expected on a laptop such as this. The problem is that my otherwise fast computer becomes wildly slow even after I'm done and Photoshop is closed. Photoshop seems to run just fine otherwise.
 
I'm using an otherwise problem-free 15'' Macbook Pro with Mountain Lion (10.8.4). Computer specs: 2.2 GHz Intel Core i7, 8 GB 1333 MHz DDR3 RAM, Intel HD Graphics 3000 (512 MB). I currently have memory usage set to 80% under performance preferences.