Concomitant means accompanying. If you run into someone that you have a crush on you might feel nervousness with a concomitant forgetfulness.
Concomitant is one of those Latin-based words you can break down into little pieces: con means with, and comit means companion. So something that is concomitant is like the companion of the main event. If you start training really hard at the gym, the main effect is that you become stronger, but there are concomitant effects, like better circulation, or a rosy glow, or getting happy from all those endorphins you’re releasing.