SPB I'm so sorry you're under stress like this. But I wonder if in addition to remedying it by meditation, herbal stuff and so on, it would be possible to address directly the cause of this trouble?
Is there not a system in place where you work (I think it's called HR nowadays) which deals with workplace bullying? No co-worker has the right to be aggressively getting at you in this way, it's unacceptable.

When I was a teacher, with many extra responsibilities, I got very stressed at times. I found that a short nap when I got home helped enormously to draw a line under the day I'd had, and I awoke relaxed and ready for my evening. If you could 'zonk out' for say half an hour, it might help your poor brain to recoup.