Yogasūtra I.38 - svapna-nidrā-jñāna-ālambanaà vā

What does it mean when we have disturbances of our sleep, or we have intense dreams or nightmares? 

Or, by inquiring into dreams and sleep, and the knowledge we can derive out of it, [can help clarify our challenges and help the mind become more settled.] 

Another strong sign that our mind is unsettled is through observing the sleep pattern and also analysing our dreams. When our mind is really settled, both at a conscious and unconscious level, our sleep will be solid, and our dreams peaceful. Hence watching their patterns can provide us insight into what is happening to us beneath the surface. Once we become aware of these, we can take the necessary efforts to resolve them, thus improving our sleep. When this happens we know our mind has settled.