Computer running slow after shutting down from overheating

Hi there,

I have a 2013 500 GB Macbook Pro, currently running Yosemite with about 158 GB of free space left. I don't have all the specs with me right now, but I can get to them if anyone thinks they'd be useful.

Two days ago, I needed to be offline for a while, so I opened a bunch of online PDF's in Chrome to read for a paper (it was kind of a ridiculous number) and then closed it and threw it in my backpack. About 2 hours later, I took it out to use it and it was absolutely red hot, even though it had been closed for a while and sitting in its case in my backpack. As I used it a little, it cooled off to normal temperature, but I didn't get rid of too many of the tabs. I then closed it again and put it back in my backpack. When I got home, the battery was completely dead and ever since, it's been running really slowly. It takes a couple minutes to boot up and when using it, it freezes up quite a bit.

Like, I'll be scrolling down a webpage (Word and PDF's are especially bad) and any time something needs to load, there's a massive, sometimes 5-6 second lag before it registers the move and the application I'm using is usually frozen during this time. i can sometimes use other applications in this time though, so it's not the entire computer freezing. However, when I'm switching a lot between applications, there can be some considerable lag and sometimes the beach ball of death before it allows me to do anything. And I've stopped being able to listen to itunes in the background because the song freezes whenever my computer is processing something.

A final interesting thing is that the computer performs worse and worse the longer I have it open. It usually works well or at least acceptably for the first hour or two, plugged in or not, after I turn it on, but it steadily goes down from there and becomes so laggy, it's barely functional. I thought rebooting it once, twice, even three times would make a difference, but so far it hasn't, and also interesting is that the only time it's overheated since is when it was on, closed, and in my backpack. Everything else seems normal. All my data is still there and the applications all work, it's just really slow and laggy.

Any ideas what's going on and what I can do about this? I can live without it for the weekend, but I really am going to need it before next week. Thanks!