I'm all about being strong and courageous and not giving up so when I cry I feel weak. But I'm not! Crying and feeling down every once in a while is normal. It alright to have those days and it's alright to not know why you're feeling the way that you are. There is always a reason but we don't always know what it is.
I had this aid in elementary school who told me that when you cry you're giving your heart a shower. Washing all the bad feelings away. I think she's right.