Ah yes, the old "cannot recognize it until you're in its oily clutch" gambit. Know it well. Fall victim to it daily. You're have a lot of company there too.
Learning how to see it coming is really difficult and may remain that way. Then one day, you do see it coming, and you respond in a more healthy manner. Then, you do it again. It's only slowly that you learn to do so consistently. Be patient and never get on your own case for not having success with this all the time.
If you have not heard of mindfulness and grounding, now might be a good time to look into it. Also, if possible, fire up a subroutine in your brain's computer that emits a little voice whenever you find yourself "in it". It should tell you raise your head and face out of the cloud of anxiety, get above it, and observe it. Other visualizations may work better for you, like imagine the things troubling you as small boulders that you can step over or around. When anxiety strikes, we tend to visualize it as right in our face, surrounding our heads, as if we're drowning or breathing its gas. The point is to change the visualization so that it isn't overpowering your senses, that its a less like a gas and more like an object you can step away from. (Hope my rambling makes sense.)
One thing that worked for me, for a time anyway, was to tell myself when I knew I would enter a potentially triggering social situation to "be ready" with an alternative visualization that I could use to not slip into "it." It was a way to replace subconscious hypervigilance with something deliberate that would help keep the anxiety at bay.
Lastly, you are right that others generally won't know how to treat us right. There are a lot of people with PTSD that feel like their on one side of a chasm and their tribe (family, friends, etc.) are on the other. We really really want them to hear us, understand us, but everything we try to say is drowned by the wind. My advice is to look on our side of the chasm (this forum for one) for understanding. This sucks and sucks big time. But I think at least in the near term, look for support where you know you'll find it.