I found a good article posted on the site Leaf Science about PTSD & Cannabis.. here's an excerpt from that article and a link is provided if you want to read more... http://www.leafscience.com/2014/01/17/scientists-explain-many-ptsd-turn-cannabis/
In a study published last month in the journal Drug and Alcohol Dependence, Dr. Bonn-Miller and his colleagues administered surveys to PTSD patients from a local dispensary to find out what exactly they were using cannabis for. Sleep, it seemed, was the primary reason.
Dr. Bonn-Miller explains that sleep problems are a big component of PTSD. Patients might have problems falling asleep or have trouble staying asleep throughout the night. Nightmares are also common.