... every night I flood my bed with tears.
One of the great things about the Psalms is that the writers allow us to know how they felt so that we can express our feelings in their words.
Psalm 6 is a very emotional Psalm; it is a real cry from the heart. The writer says "My soul is greatly troubled." That can be true for us as well at times.
It may be that you have had the experience of things falling apart in your own life. Perhaps you have done something that you know was un-Christlike and you have ended up feeling rotten and ashamed and reduced to 'tears in your darkness' as you think about what you have done. As he felt like that the writer did what we must do — pray to God that he will be gracious to us, that he will forgive us and take us out of the mess we have got ourselves into. As he prayed to God in this way he tells us how we will feel when we pray - "The Lord has heard my cry for mercy".
The New Testament puts it this way - "If we confess our sins, (God) is faithful and just to forgive us our sins and to cleanse us from all unrighteousness (wickedness)" (1 John 1:9). That truly is a wonderful promise and will make us shed tears of relief and thanksgiving to our gracious God.
Dear Lord, I confess my sins and pray that you would have mercy on me and make me clean. For your name's sake. Amen.