Macbook pro suddenly running intolerably slow

I have a mid 2012 macbook pro 750gb HDD running 10.8.5. It was working fine, then i walked to my dorm and all of the sudden it's unusually, and unusably, slow.

First I'll start out by saying this is probably not any of the first 5 problems you think it is. I'm a slightly more experienced user than I have come off as thus far.

Here is what i have checked/done:

1. I checked activity monitor. 12-14gb of RAM have been free at all times since this issue started. At pretty much all times, a minimum of 80% of the cpu was idle. I only had chrome, itunes, activity monitor, and terminal running. I ran a purge command in terminal just because I was desperate for a solution, and thought clearing inactive RAM would help, but to no avail.

2. i quit everything. i thought it was just chrome being slow at first, but then i realized everything was running slow.

3. I restarted my computer.

4. I checked my free storage space. >300gb

6. i restarted it again.

7. i restarted and booted into my windows partition (i figured maybe if i did this, then it would spend more time booting into mac, and hopefully resolve something. it was worth a shot i guess.)

8. i noticed that spotlight seemed to be endlessly indexing. probably ran for at least 20 minutes without showing any sign of progress. I figured maybe it was the reason it was running slow, so i found a sudo command somewhere to just turn off spotlight. shot in the dark. did not help. probably going to need to figure out how to turn it back on eventually.

None of the above resolved anything. Normally I just try to resolve issues myself by reading forum posts, but as you can probably imagine, this is kind of a tricky thing to look up, as 'macbook pro running slow" pretty much just yields hundreds of posts with inexperienced users asking why their computer is running slow, only to have the issue resolved by restarting their computer, or quitting out of some programs.

The strange thing about this issue is that it isn't that everything lags. The simplest tasks require more than a minute of the spinning rainbow. Tasks such as, clicking on a tab, typing a message in facebook, opening a finder window, opening force quit, and even clicking on the apple icon in the upper left when in finder. It's basically completely unusable. I have a fear that it may be hard drive failure, and i have no idea what i could possibly try next besides wait and hope the problem goes away.