MANY folks in EMS have anxiety disorders and panic disorders, and also things like depressions and I imagine there are a few with bipolar. Very few in EMS ever talk about it in the open.
It will be an adjustment period and could activate some panic attacks or an increase in anxiety. You may find that you do fine. You won't know 'til you get out and do it. And you really need to know yourself - triggers, early symptoms, and also how you respond to meds in case you need to take something PRN while at work.
I dealt with depression, panic attacks, and anxiety for a number of years (started in high school). However, I can't remember the last panic attack I had, it's been many years since I experienced a depressive episode (more than 6 years, I think). It was something that I was still dealing with when I was first getting into EMS about 10 years ago, but, lucky for me, it never impacted my work. If anything, work was therapeutic, as my symptoms were best when I had something to do.
But, despite having been doing well for many years now, I still take a low dose of a TCA and a benzo. (Based on psych guidlines, it is recommended that I stay on an anti-depressant for the rest of my life.) I'd like to get off the benzo, but right now I don't have the time to navigate a taper and any withdrawal symptoms or rebound anxiety.
As far as drug testing, I've never had a problem. Just make sure to disclose that you are prescribed a benzo so that there are no surprises.