Building a wall

I don't understand why I slip into these dark moods of mine. Even when I take such care to not slide under...it still happens eventually. If you don't understand depression, then you will never have a clue as to what I feel when I'm like this.
Now, I'm quite well known for building walls within myself. The purpose of walls is two-fold. I don't really want anyone to get in, but even more than that I don't want anything to get out. Sounds strange, I'm sure. I'm such an outspoken person, if I feel something, well, you are going to know about it. At least thats how I usually am. But not when the darkness of the depression creeps in and consumes. I could happily sit and stare at nothing for hours on end, in a dark room, with blankets pulled over my head. Have you seen New Moon? The scene where Bella is sitting in the chair staring out the window with only a mental monologue going on as the months change and pass? THAT is what I feel like doing. One telling sign for me...I sat down and watched TV last night, alone, for hours, by myself...not good, not good at all. I pull away from those that I love, I feel hurt and angry, and its not a rational thing. There is no reason for me to feel like this. So if I retreat behind a wall, no one needs to know that I feel these things, and hopefully they will just leave me the hell alone.
Today, I got out and walked in the sunshine. I forced myself to interact with my youngest in a positive way. I spent hours on homework. I'm not giving up, I have to much to live for. Life is not going to pass me by. I will work through this until I have beaten it back for the time being. It does get easier though, everytime I recognize what is going on and I beat it back I can go longer without having it come back. "It" is a part of me lol. Not a part that I really like, however, I learn something about myself every single time I go through this. So I'm still growing and learning. The song below has been playing in my head all morning...and I'll have you know, its not true, a rock does feel pain...it just hides it deep inside and has that tough outer wall so it doesn't escape.