Yeah. It's called a chemical reaction in the brain. Now, what triggers this, and for what lengths of time...? That's a whole different question, and personally, I don't think I have enough time or space to get into all the tiny little factors involved in brain functions tonight.
I heard once that when you feel sad with no discernible reason for it, it's because deep down you see things wrong with your world, or the world at large. I take that with a grain of salt, though. Anybody who can't cope with the world would surely go mad, and probably many do. But I think everyone feels some kind of existential angst like that from time to time.
Sometimes you just have something bothering you, just beneath the surface of awareness. And then it springs through, and you know where the feeling was coming from. Or it comes to you in dreams. The brain hides things from itself sometimes, usually because it's too much.
sometimes :( :)
just to many to mention :-)
Sure, just like feeling any other way. Some is real, some is imagined. Kind of whatever you're in the mood for.
Focusing only on bad things and not letting go