Why do we have sad days????

So I was sitting here at my computer tonight, and I have to say that I have a very heavy heart. Usually writing helps me, so I thought I would jot a few things down, and maybe that will help me. I am not to sure why it is that I have such a heavy heart tonight, but I do. There are so many things that seem to be bothering me, and I can't pinpoint one thing...does that make sense?? Don't know what it is. I guess I just feel as though I can't accomplish anything, and yet I know that's not true. Do you ever just feel that there are days where you simply don't measure up? I guess that is the kind of day that I am having right now. I really don't know how to fix it, except for to offer it up to the Lord, and know that He will help me through this trial, and know that tomorrow is a new day. I sure hope it's a better day, Friday's HAVE to be better....don't they????