The term yoga nidra (meaning yogic sleep) is used to describe both the state of consciousness in which we simultaneously have waking (beta) and deep relaxation/light sleep (alpha) brainwaves and, colloquially, a process for reaching that state.
The process yoga nidra is a form of reclined deep relaxation mediation typically done in savasana or supported savasana (lying on the floor). In yoga nidra the practitioner is lead through a guided meditation that includes awareness of body sensation, breath awareness, visualization, and resolution of dual experience through exploration of opposites.
Ideal for beginning and experienced meditators, yoga nidra is particularly effective for decreasing anxiety, restoring energy and inspiration, and promoting deep healing. Physical, mental, and emotional healing occurs when we experience deep relaxation and a profound sense of safety and security. Yoga nidra is an effective way to resolve trauma without discussion of the trauma itself or the symptoms of traumatic exposure.
For more on the use of yoga nidra to treat trauma, see, for example, the Integrative Restoration Institute.