Wickwire EM, Smith MT, Birnbaum S, et al. Sleep maintenance insomnia complaints predict poor CPAP adherence: A clinical case series. Sleep Med. 2010;11:772–6.
and another relevant- insomnia in PTSD:
Collen JF, Lettieri CJ, Hoffman M J. The impact of posttraumatic stress disorder on CPAP adherence in patients with obstructive sleep apnea.Clin Sleep Med. 2012; 15;8(6):667-72.