Sad for no reason?

Do you ever get sad for no reason? I mean really depressed and you can't find the cause. There are no traumatic events, no break ups, no weight gain, no nothing! Actually.. my life is going pretty well. But I am sooo incredibly sad today and I dont know why. I have people that love me, people that want me, and people that miss me. What the hell..... this really sucks! I actually resented cleaning my house today. Those of you that know me well can imagine how crazy that is.... both my grandparents are crippled and can't clean. I am a horrible person for resenting cleaning for them!! I wonder if somethingis wrong with me in a psychological way... I don't think so though, I am usually pretty happy. I am lonely sometimes... but only briefly. I have basically every material thing I want. And the things I do want are pretty much superficial.... like a flat screen TV in my bathroom, or a new laptop that is super tiny (so it is easier to take to school). Overall I have nothing to be sad about and yet all day today all I wanted to do was to sleep. crazy shit man, crazy. Maybe I am depressed becasue I am 25 and just finished my AA ..... or maybe its becasue I wasted so many years of my life. But really, I like being where I am..... no bills or real responcibility.. what the hell is depressing about that? well, I just have to remind myself how much I love me!!