Here are some articles that Anthony posted. They have helped me.
[DLMURL]http://www.ptsdforum.org/c/threads/stressor-vs-trigger-what-is-a-trigger.13912/[/DLMURL] (Stressor VS. Trigger)
[DLMURL]http://www.ptsdforum.org/c/threads/triggers-the-core-root-before-symptoms-are-activated.13861/#post-213834[/DLMURL] (Triggers--the Core Root Before Symptoms Are Activated)
[DLMURL]http://www.ptsdforum.org/c/threads/what-is-a-flashback-a-flashback-is.13876/[/DLMURL] (What is a Flashback)
The articles above have helped me to better understand what is happening during triggering moments as well as flashbacks.
Thankfully, I almost always only get stuck in flashbacks when I'm heavily dissociating for long periods of time. Usually if I haven't dissociated (when I say dissociate, I mean all of my senses are completely muted and I am paralyzed by this effect) in a while, I don't get flashbacks the first 2 or 3 times I start up again, but after a few goes I usually begin to dissociate and then slowly become consumed by a flashback before I can do anything to stop it. I have combated these flashbacks by combating dissociation. Unfortunately, my most effective grounding technique is smoking cigarettes. >.< I don't recommend this.
However, there are several other ways to ground yourself, and I find these tools of being present invaluable to helping with triggers, flashbacks, and dissociation. I think a lot of it has to do with focusing on your surroundings: bare facts. I am in a room. The walls are white. X, Y, and Z people are here. This is what they look like. This is what they are doing/saying. There are seven items on the coffee table: a, b, c, d, e, f, and g..." etc. Stressors do not generally go away by just staying mindful and present and aware of my current place and condition, because they are just that: stress. It's just stress that makes everything else harder to cope with appropriately. Triggers, however, bring you back, as do flashbacks, as I'm sure you know. If you are being triggered or you are flashing back, you are not being mindful and present, because you are going back in your mind to your trauma(s). When you feel yourself going back, do whatever will help you to stay in the moment. Sometimes a relaxing drive will help me shake off what I'm feeling if I am continually triggered over a period of time, whatever the cause may be. I think that identifying triggers as triggers is very helpful, but I also believe that you can still have ways to cope even if you don't know exactly what is triggering you. Driving forces me to be aware that I am in a state of transition, movement--I am not static, the way I feel when going back mentally/emotionally to my trauma. I do not recommend driving if you are having serious problems flashing back or dissociating, and of course if your trauma is car-related, this is unhelpful!
I hope that this has helped to lend you some clarity. Good luck.