It is normal to feel traumatized by violence, especially the sort inflicted by police in such situations. I suspect part of this is that as much as we know that the cops aren't our friends, most of us have grown up with a mixed bag of signals about this. Combine that with the reality that the cops essentially have carte blanche to deal with people during demos, and it is a recipe for terror.
I really like dot's suggestions for ways to hopefully preempt feelings of fear in the future, and agree with her critiques conflating arrest and cd type non-compliance with direct action.
I also think clodbuster's answer rings true to me. there are times I have risked a lot because it didn't matter or seemed worth it based on my own internal balance sheet, and there are times I hung around too long because I felt like I ought to, and regretted it. Frankly, when I went with my gut and risked more I've come away better off than when I went with my internalized spooks of morality, which mostly left me feeling pissed at the other folks I was with and disempowered, even if the latter was seen as a "victory" and the former a "loss" by my peers.
Trust your gut on this. That doesn't mean don't take risks, it means do it when it is right to do it. Also, the opposite is true - it is okay to dip out if things start to feel to hectic (just be smart - cops like to pick off individuals).