Playing a LAN game with one other player, I was in creative not doing much with him in survival walking from a few chunks away towards me. I noticed my CPU use percentage for my computer was in the 90s, and since Minecraft was the only program running, I started up jvisualvm from my jdk bin to see if I could figure out what the problem was (screenshots attached). After a while I started to try to do some CPU profiling of the client.main.Main, but after a few minutes of seeing my CPU at 100% almost constantly I told the profiler to stop, resulting with an error (see the first screenshot). The Minecraft cursor was still blinking in the chat, so I thought it was still running, but I had forgotten the buttons to press to cause a crash for a report and didn't want to open a browser to find out, since the CPU use was still high. After this happened, I closed Minecraft and took the other two screenshots. I noticed on the end of the Main graphs erratic behavior. I also noticed that the first two 100% spikes on the Main CPU graph seemed to line up with changes in the threads graph.

A few days before the above happened I left the game open to LAN so my brother could play while I was at work for four hours (it was the only program running). He was still in the game but left the computer to come to my room and saw that my computer was 'steaming' and was making a noise as if a CD was jammed in the drive (there was no disk inside). He noticed that the screen appeared normal but the other signs made him turn off the laptop. He felt at the built-in fan vent and it was really hot but did not actually burn his skin. I returned home later and the computer worked as usual. (There's a cooling pad with two fans under the laptop, this might have helped.)

I'm trying to be as helpful as possible, I've never done a bug report before and am not sure if I gave everything I could; if there are questions I will try to answer them if I can. This one seemed serious due to what happened to my computer so I made an account on here to report it.
Another note: this computer can run Skyrim acceptably (for me anyway, it's better than minimum settings) and I've never had a problem with Minecraft before, so I don't think it is a computer problem.