There could be a few things causing this:
1. Background process - Make sure that you don't have a lot of background process running while your game is running
2. Start up programs - These will start every time your laptop starts and will run eating the ram when you are playing the game. Turn off any that is not needed
3. Anti virus - Some anti virus software are resource hogs, if you find that it is taking a lot of ram, then choose a lighter one
You could try and put it on a cooling pad and see if its happening. I don't think its hardware related as the gtx 860m is quite strong enough to play the games you have mentioned. Try the above and get back to me