Wil Pigeon: Well, they're so related that two of the primary features of PTSD are sleep disturbances: nightmares and insomnia.
If you think of PTSD as something that creates hyperarousal in the mind and body--the mind thinks a lot or over thinks and the body is overly active--both of these things are not necessarily conducive to sleep.If someone in this state is trying to lay their head down to fall asleep, we have a recipe there for trouble falling asleep or potentially trouble staying asleep.
In addition, sleep can be disturbed by nightmares.
A nightmare, as most people know, is a bad dream that we waken from and have an emotional response. When that occurs, there's an opportunity to first disrupt sleep, and then spend a longer time awake because we're emotionally charged. For some folks with PTSD, there can be several nightmares and repeated awakenings throughout the night.

The film Stop-Loss dealt with issues of PTSD, among others.
The frequent nightmares that can occur in people who don't have PTSD are not necessarily any different from the nightmares that occur in people who have PTSD.
The difference between can occur with or without nightmares; having PTSD doesn't necessarily mean you're going to have frequent nightmares. In fact, only about half of people who have PTSD complain of having frequent nightmares - even though we think of traumatic nightmares as the hallmark of PTSD. It just so happens that nightmares is one feature.
In the general population, between 2-5% have frequent nightmares, whereas about half of those with PTSD will have frequent nightmares.
Someone who’s experiencing nightmares should first realize that it is a regular feature of having experienced a traumatic event. Initially in the very early stages, having nightmares about the event can potentially be useful. When the nightmares start to be very repetitive, that’s problematic.
When that’s the case, there are again two approaches: medications and behavioral therapies. While there are no approved medications specifically to treat nightmares, there are two medications approved to specifically treat PTSD (which can be helpful for nightmares). That is something one should speak with their physician about.
The other approach are behavioral strategies; the most widely used one is called Imagery Rehearsal Training (a.k.a rescripting therapy). In general, it views nightmares as a thought process that can be changed. Folks write out their particular nightmare or recurrent nightmare, rehearse it, either by reading it out loud or to themselves, then change something about the plot or description. What happens is that after enough daytime practice with this approach, the nightmare will change.
This may seem like a Hollywood-type approach, but in fact, it’s based on some pretty sound work; in general, this approach has been found to decrease the intensity and frequency of nightmares.
The Deer Hunter was one of the first Vietnam-era films to address that war and PTSD
We have really good treatments for insomnia, both PTSD and non-PTSD related. In general, there are two kinds of treatments: medications treatments and non-medication approaches, the most popular and most effective of which is called Cognitive Behavioral Therapy for insomnia (CBTi). Both approaches work for insomnia that isprimary, and insomnia that is co-morbid or co-occuring with other conditions such as depression, anxiety, chronic pain, fibromyalgia, and PTSD.
We treat insomnia in the context of PTSD with the standard forms of treatment though with a caveat: insomnia present with PTSD is unique, so there are additional things we need to keep track of and address. In PTSD it is often that case you have insomnia and nigthmares, so you must also include nightmare treatment.
If you suspect that you or someone has PTSD, the first thing to do is realize that this is a a well recognized physical and mental disorder. Realize:
I might have this thing, it's a real disorder, I'm not making this up, and it can have pretty lasting effects, so I need to get it assessed and treated.
The best place to start may depend on where you currently receive care. If that's with a primary care physician, then they can refer you to treatment for PTSD. If you happen to have some form of psychotherapist, they may direct you to people who specialize in PTSD treatment.
Dr. Wil Pigeon is the author of Sleep Manual. He is also the Assistant Professor of Psychiatry and the Director of the Sleep & Neurophysiology Research Lab at the University of Rochester.