Can't write properly?

Lately, for the past few months or so, I've been unable to write straight when taking notes in class and whatnot. It's almost like an extreme version of distressed keyboard-mashing. I'm sitting there taking notes, usually feeling somewhat depressed, and then an intrusive thought or memory appears in my mind, and it has a physical effect on me. I immediately dissociate for a moment, gasp, and my hand goes tense, leading me to draw my pen in a straight line away from where I was writing. Sometimes my hand drags the pen so hard it tears the page. Today it was particularly concerning, since it happened 5-6 times in one class, and I was actually enjoying myself in class discussion. It's pretty annoying and as a result my notes are riddled with these gashes through the pages of the notebook.

Does this happen to anyone else? Anyone know what the cause is? I'm not sure if it's because of BPD or something else.