That explanation sort of makes sense, as I was sequencing when I was visiting my brother (I'm an early riser), and when I brought it home, I turned on the laptop and plugged it in, but the power bar was off. After I realized this, I turned on the power bar, the icon in the system tray changed to show that the laptop was plugged in and running at maximum performance, the battery started charging (from 80%), but it was still laggy for a bit but magically went away after a bit. Perhaps you don't get full performance when plugged in until the battery is back up closer to 100%?
But I'm pretty sure I also had this issue last year when sequencing, and the laptop stayed in the same spot all year. Who knows, maybe it wasn't plugged in, and I didn't consider that running on batteries it would be an issue at that time.
If I run into the issue again with a plugged in laptop with a 100% battery, maybe I'll bring up the question again.