Recently, there has been interesting research about the role of safety signals in PTSD (Post-Traumatic Stress Disorder). It seems that when people are able to learn about safety and create that in their minds, they are able to get more REM sleep which helps them heal from the traumatic event. This is an article that contains a synopsis of that research:
One of the ways that I like to create safety for clients is with EMDR. I do what is called “resource” work with “installing” a safe person and a safe place by using bilateral stimulation (eyes going back and forth, alternate tones in the ears, or tapping the hands alternately) while the client thinks about a safe person and/or safe place. What is meant by “safe?” I usually encourage the person to think about a place where nothing bad has ever happened to you, and that makes you feel calm, happy and peaceful while you think about it. Similarly, for the safe person, it should be someone who has not had much conflict with you and who is dependably considerate of your needs and desires, hopefully even helpful to you. I have had many people tell me that this helps them feel calmer and less anxious or stressed when they practice thinking about the safe place or person regularly. Sometimes when we have less stress, it makes sleep that much easier, whether or not we have post-traumatic stress.