Anthony Lusvardi, SJ, thinks that repetitive prayer is often just what we need:
While these “formal” prayers are often learned in the most mundane settings—before going to bed as children, in catechism class—once they become a part of our spiritual language they often become the prayers we fall back on in the extreme moments of our lives, moments of fear and anxiety. . . . There are times when we know we need to pray but we can’t think of what to say. The important thing in such cases may not be the words themselves but our need for God.
One way to approach repetitive prayer is to chant it. Once I began chanting Psalm 23, I found that it lingered in my mind throughout the day.