This particular nightmare keeps coming back

Dear DS diary,
I'm still having trouble sleeping through the night.  I keep waking up in the middle of the night, and it's usually rough enough to keep me awake for at least two hours.  It's small wonder that I haven't been functioning too well lately.
The following nightmare in particular refuses to go away on me; it has kept coming back, with variations on what happens.  I e-mailed it to a friend last night, only to see it come back once again, so I guess I now have to leave it here as well.
Clearly, it's a double retrigger because of the anniversary of the marathon bombings, which in turn is rekindling the day my high school was smoke-bombed.
Here's the nightmare, as it was told to my friend:
I'm in the downtown section of a major city, lined with various streets and restaurants.  It's an area I've been to before, and experience had been telling me that this was a fairly safe place to go.  The street is busy; there are a lot of people around and by extension a lot of activity.  Occasionally there is some automobile traffic, but since there are metro (subway) stations in the area, most are preferring to use the public transit system.  Most of the activity is therefore foot traffic.  Everything looks normal.
 
But nobody, including me, realizes that a time device has been planted underneath one of the trash cans on the street.  In an instant, and quite suddenly, the device detonates, blowing the trash cans to smithereens and creating a huge fireball.  It sets one or two of the nearby buildings on fire...and I'm unlucky enough to be near the spot where it goes off.
 
At this point, the nightmare has taken several different tracks on me, which is probably how it's been recurring so much.  In one, I get caught directly in the blast and am killed instantly.  In a second, I don't die, but I'm pretty badly hurt...I end up spending several months in the hospital because I need a prosthetic leg -- or both legs -- and the way I lived my life as I knew it was over forever.  Or I'm not that badly hurt by the blast, but am so shaken by the notion of seeing a bomb go off that I develop paranoia and end up committed for the rest of my life.  In a third, I'm just far enough away to not get hit by anything, but I can't get away or look away fast enough to avoid seeing all the carnage it causes...corpses, wounded, blood all over, a horrific scene.  I get so scared that I'm powerless to do anything else.  I feel like I have to run into the fire and just end it right then and there, because I know I will be living under a rock for the rest of my life after witnessing this.  Again a couple of variations have taken place.  In one, I actually do kill myself by running into the fire.  In the other, I know better than to run into the thing, but I also feel like I have to flee far, far away; out of the country in fact...except I don't know where to, because now I feel like I need body armor, a giant Arabian sword, and an AK-47 just to protect myself.
 
That's what I can distinctly remember from this nightmare.  It's at that point that I wake up, and then I can't fall back asleep for hours.  Sometimes I can't go back to sleep at all, which is ruinous because it's usually waking me up at somewhere around 1am or 2am, and the sleep loss it's creating has caught up with me.
 
Logically, I realize that the odds of the nightmare actually happening are at best a very big longshot.  But emotionally, it has hit home with me that this can happen anywhere, and it has been really hard for me to come to terms with the vision that anybody I don't know could do something like this.  It's feeding my feeling that people are out to hurt me and I don't know how I can change that feeling.