First off, ask as many questions as you want man. You may have some that sound silly or ridiculous, but again, we've all been there. When I started seeing a therapist, one of the best things about it was just being able to talk really freely without worrying about someone thinking you were losing it. I'd encourage you to do the same here.
Anyways, yeah I had issues where my left arm felt weak. Everything started for me with my left hand. My index finger started twitching one day at work and it freaked me out. I made the mistake of googling that and like a moth to the flame, immediately was drawn in by the ALS search results. So yeah, for a few weeks I felt like my left hand was weak or that my left shoulder was weak as well. I went as far as to start measuring the size of my forearm and biceps and comparing that to my right arm (I'm right dominant as well). I'd lift weights with my right arm and then test my left arm. I was constantly trying to open jars with my left hand, squeeze paper binders with my left fingers, anything to test the strength in fear that it was suddenly going to be less strong. I'd go to bed at night in fear that the next morning my left arm would suddenly be useless. Your mind can play really crazy tricks on you and the hardest part for me was accepting that it was anxiety. I'd always thought of anxiety as that nervous feeling before a test or interview. So it took me a while truly accept that it was anxiety. Doctor put me on citalopram as well (generic version of celexa). Don't know how long you've been on it, but it takes a while (3-5 weeks) to fully start feeling the effects. My advice with that is too look at the meds as just one tool in fighting the anxiety. They help, but they won't alone help you conquer it.
I did change my life style. I cut out almost all caffeine and started doing yoga type routines in the evening. Work was especially hard for me. I'm in front of a computer almost all day and so it created ample time to look up the wrong things on google and to just space out in my fear and negative daydreaming. I had to start literally writing down a list of what I needed to accomplish each day and tackle each one by one. A lot of times, that sense of accomplishment alone helped a lot. For a while I tried creating a worry time. I kept a separate note pad that I'd write down my worries and fears and then everyday at 3pm I'd address those. Most of the time they seemed silly by the time I got around to reading them. But I started out having more bad days than good, then it started to even out and then I starting stringing more and more good days together and so forth. I wish it were a quick fix but for myself, it just took time. Hope this helps and feel free to shoot me a message if you have any other questions. Good luck.