Of 100 people polled, those who went to bed later and slept for shorter periods had the most severe symptoms of worry and negative thinking. Although anxiety can contribute to sleep problems, it's also possible that inadequate sleep or divergence from natural light and dark cycles makes it harder to inhibit troubling thoughts, Nota and Coles say. They cite other research showing that among people taking antidepressants, cognitive behavioral therapy for insomnia can help reduce depression.