Hello again!

I've been playing ARC/BRD a bit now, and lately I've begun to notice that my toon seems to be losing health seemingly every time I attack a target during boss fights? I've watched it happen both in Haukke Manor and in Brayflox's Longstop and I have no idea what's going on with it.

I have no debuffs on me, and nothing is attacking me. Have I missed something?