You might hear: "What if something bad happens?" "What if I cannot sleep?" "What if there is a fire?" The worries at this age are often more specific and more cognitively developed than in younger children, and they are no less real for that. The mind at this age is capable of generating elaborate worst-case scenarios, and the quiet of bedtime gives those thoughts space to expand. The self-talk is running interference.
Your brain is doing what brains do at night, generating what-ifs. Let's work with it instead of against it.