It's unlikely to be (true) buffering. I suspect that something is grabbing your system's resources. (I've experienced problems with Microsoft Security Esssentials' updater, MsMpEng.exe, slowing computer to a crawl, for example).
Start by downloading, installing and running the free version of Malwarebytes Anti-Malware:
https://www.malwarebytes.org/free/
There might be some malware causing the problem.
Then, before the problem arises, open the Task Manager (via right-clicking on the Task Bar at the foot of your screen) and click on the Processes tab. Maximise the window and the minimise it to the bottom of your screen. When the problem arises, immediately click to bring up the Task Manager again and look down the CPU column. Anything in double figures should be noted and treated as suspect. Then look down the Mem Usage column. Anything really big should be treated as suspect but (most importantly) anything where the figure keeps changing (even if those figures are actually quite low) should also be regarded as a possible problem. (That's how the MSE updater shows up, for example).
Let us know if you find anything odd.