Lament is a model God gives us to deal with the bad stuff that happens in life. The Bible depicts many lamenters (think: Hannah, Job, David, Jeremiah and other prophets, and Jesus!) and even God laments through His prophets. It is normal to feel pain and to bring it to God. He wants us to seek Him in our pain. Feeling down is not a sin, nor does it indicate a lack of faith.
The Bible tells us there is a time to be happy as well as times to weep and mourn. These 'times’ are out of proportion in our American culture that encourages us to only show the happy, not the weeping. Sometimes we focus so much on being happy people (especially on Sundays), that we try to skip over any sad or angry or grieving emotions we may feel. We don’t allow time to feel negative emotions. Lamenting is how we trust God with our pain. It is how we trust God with others’ pain. Lamenting is deeply human.