Dude I have the exact same issue as you, regarding your anxiety. For me though it's the right arm. My symptoms are kind of like tennis elbow, except I only have a mild pain once in a while when doing certain motions with my right arm/wrist/fingers.
Also, when I hold my left and right hand together (like when you're praying), and I try and spread my fingers as much as possible, I can see that my left hand is slightly more flexible than my right. On top of that, I also feel some minor tightness in my wrist and forearm that comes and goes. I also have fasciculations all over my body, arms, legs, sometimes hands, eyes, chest and back) rarely in the tongue though. They're not present 24/7, but they do come frequently throughout the day, mostly when I'm sitting down or in my bed.
What really kickstarted my ALS fear, was when I learned of atrophy and fasciculations! I started checking for symmetry in my muscles constantly, and I noticed that when I press my forearm against my bicep (just like when you're flexing your bicep), turn my arm (so that the fist is pointing at the chest/neck) and then flex it (while turning my wrist away from the chest), I have a dent in my skin close to the outer elbow. I checked my left arm too, but the dent was not as noticeable as on the right arm, and then I panicked.
I went to the neurologist 2 times and had some blood tests done. They were fine thankfully (CPK not elevated in case of atrophy). He also did a series of reflex and strength tests, and they were all normal as well.
However I'm still kinda worried, as I sometimes feel like my dexterity is decreasing in my right hand, but sometimes it's like it's normal. I really hope that this is all in my head though, and I really want to get an EMG just in case, but I'm not sure how to tell my doctor without making it seem like I've gone completely nuts (he knows about my HA, lol).
Anyway, I guess the point of this post was to lighten your mood a little bit, and to tell you that you're not alone with your fears. But do also keep in mind that prolonged anxiety can lead to stress, and as a result it affects your nervous system, which might be the reason that some of us get benign fasciculations (however I'm not a medical professional, this is information I've gathered from my Neurologist and on the internet).
Try and set off 15 minutes of your day at a specific time, to sit down and reflect upon your fears/worries. For example at 17:00 PM to 17:15 PM or something like that. If you're out of this time frame, just tell yourself: "No, I can't think about these worries right now." Tell your fearful thought to take a seat and wait until it's 17:00 PM. It might sound a little cheesy, but by doing this, you're forcing your focus away from the negative thoughts. It might take some practice to get used to, but I've had some good time practicing this technique
.
Anyway, happy thoughts.