Tina, YES! I've dissociated at work (which looked like me just staring through my laptop all day), and gotten triggered badly enough to go into the stairwell and sob by myself. And it's okay!
I think self-compassion is the most important part of recovering from these things. You aren't a bad employee. You had a rough mental health day. We all have them, some worse than others, and it's okay. Rather than apologizing, I think we should cut ourselves some slack. :) If mental health struggles are becoming noticeable at work, and you're comfortable disclosing, you may want to consider sharing with a manager or HR person there. Perhaps together you could come up with a plan for avoiding triggers at work, or ways to de-stress when you are triggered.