Apple Hardware test freezes, MacBook Pro freezes for no reason from time to time: hard disk problem?

Hi,

So first of all, I own a 13" mid-2012 MacBook Pro with a 2.9 GHz i7 processor and a 750GB SATA 5400 rpm hard disk. It's running the Mavericks 10.9.2 OS X.

This is going to be a long post, my question is basically whether or not my hunch is right about my hard drive, and whether or not I should consider investing on an SSD. I just wanted to be thorough with what happened.

So almost two weeks ago, I dropped it from about 2 ft. high. I used it normally for the next 5 hours after that. It ran perfectly then. At one point, I was downloading a lot of things simultaneously, I had about 10 tabs open at the same time, and it froze. I did not make a big deal out of it because I thought it was just me abusing it. So I forced it to shut down, and when I tried to restart, it wouldn't let me get through the log in screen. I kept on forcing it to shut down, and restarting it—and each time it would let me go through little by little until I was able to actually log into it and see my desktop, albeit very very slowly. I let it rest over night.

The next day, I was able to load my desktop, Finder to check if my files were still in tact, but it wouldn't load random things like the Dashboard, for example. Every single time I wanted to run an app, the cursor would just keep on turning for 5 minutes before the app ran.

I started to run the Apple Hardware Test on start up, and for the short one, it froze at 1:55; and for the more comprehensive one, it froze after about 25 minutes.

I backed up all of my files, took it to the Apple people here in Denmark (Humac) and they said the hard ware was fine and it was an unknown software problem. So they wiped up my hard drive, and reinstalled the OS X. It worked fine after that.

I don't know if I'm just more aware of the sounds my laptop makes out of paranoia, but my hard drive keeps on making clicking sounds, even if it is sitting still on a table.

3 days after the repair, while I was watching a YouTube video, it started to freeze again. My dock disappeared, even though the video was still playing, and I couldn't shut it down properly so I forced it to shut down again. This time, when I tried to restart, I just saw a grey screen. I tried to disconnect everything from it, but nothing—still the grey screen. I ran Disk Utility from start up, and the disk couldn't be verified nor repaired. This time I actually did what the Apple people did the last time—I wiped my hard drive clean and I reinstalled the OS X, and then recovered my files.

Now it is running fine, but I have a feeling that it is a hard drive problem and it will freeze again at some point. Now the disk can be "verified" on disk utility, and it says that it is working fine. The Apple Hardware test still freezes at 1:51, and it can never complete the more comprehensive check. I am considering to invest on an SSD and do the installation myself, but I don't want to do it unless I am 100% sure that the hard drive is the problem.

Any opinions? Is it Mavericks? Could it be the drop that damaged it? If so, then why is it still running now?