What Goes On In Their Mind?

So there's this person in my school; now who this person is or whether it's a boy or girl, I'll just keep that to myself...but this person has a [slight] (if not bad) mental condition.
Now when I say mental condition, I don't mean special needs or something along those lines, I mean the type of mental condition that can affect their mood, the things they say, and possibly how they see things (or maybe their ego).

In this case, one main thing this person's mental condition seems to affect the way this person treats other people. One moment, this person may be nice, and the next moment,they'll be treating the same person differently than before and start acting like an a-hole or a b**** to you (depending if it's a boy or girl of course..)
Because this person has done this to it's various friends amongst school, from what I know he or she has pushed those friends away; to an extent that this person's true friends are only said to be two people in that person's year (one of which is a new student)

Another thing this person can try do at points is try and put others down for whatever reason...this I don't understand; if you were at that time depressed or sad at one point why would you want someone to feel the same way? If this person needs to bring someone else down (who most probably doesn't deserve it) just to bring themselves up, then their mental condition may be a bit worse than it seems (either that or they're slightly twisted)...I don't know, maybe that person has the same mindset as whoever left bad comments on one of my previous posts...

Or maybe that person is just insecure about themselves, however that shouldn't be an excuse.
I admit it, I'm very insecure about myself, but that doesn't give me the right (or the excuse) to try and bring others down, just because I'm personally in a crappy mood. If I was to be in a bad mood, the last thing I'd want to do is to try and make someone else feel the same way...perhaps this person doesn't want people to see them as insecure, perhaps they'd rather have that affect on other peopl, just so they can forget about their problems for that moment...

Now I've seen this person in many states; I've seen this person be nice, I've seen this person be horrible. I've seen this person being social, I've also seen this person being the complete opposite, refusing to talk to almost anyone. I've seen this person in many ways, but in one memorable state I've seen this person in is when they were crying once at school. When seeing that person cry, I realised this person isn't as mean or as tough as they [might] seem at times; it got me wondering, is this their real personality I'm seeing? Is what they're usually like at school all an act? I can definitely say that day I saw a different side to that person; a side I didn't really know existed in them.

I don't want to give the impression that I hate this person, because I don't; if anything I can't help at times but feel sorry for them and pity them a bit. They can't help their mental state; but this mental condition they have has the potential to affect how that person's peers see them (and not necessarily in a positive way)...
I also don't want to give the impression that I know all the answers to this person's issues, because I don't...I'm just saying what I think and how I see it from my point of view...What this person's condition is called I don't know, but it could be a number of things...could this person be slightly bi polar, a potential future schizophrenic, or are they just paranoid at times? Who knows...

What I do know is that they have visited this blog before, so they probably might read this; so if that person knows I'm talking about them then this is what I want to say to them now:

Stop the act; or if it's not an act and your condition makes you have split personalities, then get help. I'm not saying that you should visit the school counsellor (I don't think even she can help you...no offence) but maybe a few therapy sessions or something, because you don't seem to realise how your condition can affect the way you are seen sometimes. Or maybe your split personalities (if you have them) make it seem that at times there is nothing wrong with you to people like the school consellor, when that's not the case. You can allow others to help you if you can't even help yourself a tiny bit.