Mind Games

So, I'm curious into how our minds work, and why/how we think about or dream about things that we shouldn't, or don't want to, or haven't even thought about...  What causes mind games, and what purpose do they have? 

Early this morning I dreamt about a person that I didn't want to dream about, not sure why I dreamt about, and woke up with a complete "wtf" moment...  This person brings up too many memories, things that I have worked really hard to forget.  Ok, forget isn't the right word exactly, maybe put out of my mind (who says you have to forget, just locked away).  This person shouldn't even have a moment of my time, and definitely shouldn't even be a thought in my mind.  So, why out of nowhere do I dream?  I didn't think about this person this weekend, and I certainly didn't expect to dream about them, so why now?  And why out of no where do these thoughts emerge?  Just wondering...

And why are my dreams always about things I don't want to think about or remember?  Where are the happy ending, fairy tale dreams?  Where are the beach dreams, vacation dreams, candy cane and merry-go-round dreams?  How come I don't have those types of dreams?  But no, mine have to be depressing, about people I don't want to think about, people I shouldn't think about, so what kind of mind game am I playing on myself?

So, today I face the world somewhat irritated, and I shouldn't be, more like what are you doing to yourself and why?  What inside me wanted that dream, because the majority of me is saying leave me alone, don't invade my thoughts, my dreams, my life... you've already wasted too much of all of them, and don't deserve a minute or second more... So how do you stop the mind games?  Where do they come from?  Why do they exist?  Again, just wondering...