Your laptop is telling you that it is time for a very thorough cleaning. You'll want to address this soon as continued heat episodes will degrade your components quickly.
You (or a local shop) will need to disassemble the laptop and clean out the heat sink vents (at a minimum). I would also suggest using that time to reapply thermal compound to the CPU and GPU - YouTube is a great source for DIY disassembly instructions, https/www.youtube.com/results?search_query=m17x+r4+disassembly see if it isn't something you want to try to do yourself (not too difficult). If nothing else, you'll have an idea of what the shop should be looking to do
Just want to let you know that I have the same model and started having the exact same problem a couple of weeks ago. The machine worked fine for nearly two years (well, one memory stick went bad but it was under warranty so got replaced free) and then I started getting the dreaded "Gray Screen of Death" consistently after about an hour of playing games. I tried cleaning out the system myself with compressed air as best I could, but it's still doing it. Dell Support wants me to send it in so they can have a look at it. I suspect the fan on the video card is not functioning properly. It passed Dell's pre-startup diagnostics tests but I noticed while gaming that often don't hear it running at all--which would explain why the GPU overheats.