Important note: I recognized I wasn't feeling well, and did something about it. I looked at my materials from therapy. That enabled me to get a few important things done, which relieved some stress and made me feel better.
At school, I moved out of the quiet study room, and into the great room of the library where I sit with people from my classes either at my table or in close proximity. You'd think, with PTSD affecting one's ability to concentrate, that noise would be a problem, and sometimes it is-- there are times when I'm tired and stressed, and the noise becomes too much. It does happen. I get triggered the most, I think, when I'm at a table alone.
For those times, I changed Pandora stations.
I had been listening to ambient, mellow, quiet music, thinking it would aid concentration. Sometimes yes, but mostly no. Now, I listen to stuff like Linkin Park, Papa Roach, etc. while I study-- and here's why it works:
To ground, you want to use the five senses (sound, touch, smell, taste, and sight). To connect with the here and now, you want to do something that will bring all your attention to the present moment. A couple of grounding techniques are described below. Sound: Turn on loud music
Loud, jarring music will be hard to ignore. And as a result, your attention will be directed to that noise, bringing you into the present moment.
So maybe it's not that I can't always concentrate, as it is that I'm not always "here"-- if my senses are tuned in, isn't that the opposite of disassociation? Whatever works...