You must be reading my posts. They have that effect on women.
But cereally, that's not a good sign. It's most likely your battery heating up. How old is the battery? Might want to pull it out and run strictly on AC until you can replace it. They can melt or worse.
EDIT -- wait, Sonny's right here, right on the money:
You're going to fry the lap top. It has to vent from the bottom. Do not cover up the vent slots on the bottom. They generate a lot of heat. They have to vent through all the holes and slots.
I learned this years ago when I had the laptop on a sofa and it just shut itself down. The repair guy essplained it. Always keep a space under the thing, preferably a cooling pad is even better, even if you don't run the cooling pad fan, because it's designed to allow air flow.
Even as we speak I have mine as usual on this one, I love it:
Now this one's pricey and has built-in speakers, which you don't have to have, but they sound great, and it's durable. And very very comfortable.