Brief summary of evidence supporting the efficacy of biofeedback for insomnia:
Yucha and Gilbert (2004) state that in 1996, an NIH Technology Assessment Panel examined existing research and concluded that several non-pharmacological techniques, particularly relaxation and biofeedback, produce improvements in some aspects of sleep, but questioned whether the magnitude of the improvement in sleep onset and total sleep time were clinically significant. In 1998, the American Academy of Sleep Medicine recommended biofeedback along with progressive muscle relaxation for insomnia after reviewing the quality of research, using American Psychological Association research criteria. Biofeedback was rated "probably efficacious" along with sleep restriction and cognitive-behavioral therapy. (Morin et al., 1998) (Progressive muscle relaxation, stimulus control, and paradoxical intent were rated even higher.)
* Much of the information provided here is from Carolyn Yucha and Christopher Gilbert's 2004 book "Evidence Based Practice in Biofeedback Neurofeedback" AAPB, Wheat Ridge, CO.