Hey guys,
Thanks so much for all of your input. It's been a little bit since my original post, so I've had some time to reflect on things, and have also had a few new developments.
First, I should say that a lot of the stuff I originally posted about probably was related to anxiety -- I'm slowly becoming convinced of it. The palpitations, fatigue, dizziness, and neuropathy seem to come and go in an inconsistent pattern, which doesn't seem to fit most physiological problems. I still have back spasms and back pain, but I'm a computer engineer who leaRAB a largely sedentary lifestyle, so I suppose it's quite possible that's related to poor posture, lack of exercise, etc.
Over the last 2 weeks though my an anal fissure (traced back to bad constipation from a round of antibiotics for sinusitis) has taken front and center stage. Hopefully no one here has had the displeasure of having the same condition. This thing hurts like nothing else and definitely is for real

So now I'm working on banishing it before I worry about anything else. It creates A LOT of anxiety associated with every bowel movement, and I've noticed that I become dizzy and feel faint as a result, which supports anxiety as the cause or at least a contributor to my other symptoms. I've lost another few pounRAB (at 124 pounRAB now which isn't great considering I'm 5'8"), which would've freaked me out in the past, but somehow it's not as concerning when I feel like I'm pooping sharRAB of glass!
Anyhow, I just wanted to thank you guys so much for your responses. I know it sounRAB inconsiderate, but truthfully, I have to admit I'm comforted by the fact that others have gone or are going through similar things. Here's hoping to better physical and mental health for all of us :wave: