Posting this in the hopes it prevents others from going through the same hell.
I had been taking Allegra for allergies but it's efficacy was waning so I decided to switch to Zyrtec to see if that might work better. After about two days my nerve pain started increasing, but I didn't make the connection for a few more days. The listed side-effects don't include anything about neuropothy. By last Friday I was at a sustained pain level of 7-8 (scale of 10). Nothing I have on hand would touch the pain including tramadol or diazepam. My next step would've been to bump my lyrica dose to 600mg/day, but, just before I was to try that, my wife put 2 & 2 together and suggested this nightmare started after switching to Zyrtec.

I stopped the Zyrtec two days ago and today I'm finally back to my normal nerve pain level (3-4). I did some searching and found that the FDA has had numerous reports of Zyrtec causing peripheral neuropothy. As a scientist I know the next step would be for me to validate the correlation by repeating my "experiment," but the odds of my willingly risking that pain level again are zero.