While I'm having a similar issue, for me this only occurs when my laptop, an HP Stream 14, is plugged in and charging, especially if I'm not using anything due to a background process' activity. That depends on the processor speed,
the CPU utilization, and the amount of threads currently running on the system.
As soon as the utilization reaches 100%, within 3-5 minutes the CPU utilization and processor speed limits and is descended by 2%-9% 0.08-0.80 GHz every 3 and a half seconds, decreasing the number of threads currently running. As
soon as it reaches to 7% 0.11 GHz or 5% 0.08 GHz (and rarely, 3% 0.05 GHz), the performance of my computer is affected and everything (including my PC) becomes unresponsive until I hard-reboot the machine (which may work sometimes, but usually not).
I don't think my computer is reliable enough. And anyone experiencing the same issue should report their symptoms here.
Oh, and one more thing: Check the Performance tab in your Task Manager. If you see the blue line slowly descending, and X.XX GHz is dropping at its rate, your computer is likely willing to slow down and lag a lot.

Either restart your computer (in the hard way) or close all affecting applications.