Well, we certainly can't rule out that it was herxing, depending on the exact timing of things. Did you just restart your treatment when it happened? Within a week or two? That could definitely be herxing.
If it was a cold (but only for 8 hours? Still makes me think that it was herxing, and the Epsom salt soak helped tremendously), that means that your immune system is working well enough to not only recognize the virus, but to send 'attackers' after the virus, which causes symptoms. This is a good thing for those that can verify that they had stopped getting colds even after they have been fully exposed to the virus and didn't get symptoms, because it shows that the immune system is working well enough to recognize and go after the virus, which it wasn't doing previously.
But, considering your cold only lasted 8 hours, it's more likely that it was a herx. Colds usually last at least a few days. Are you doing any other regular detoxing? It may not be enough. I would encourage you to increase your detoxing. If you need suggestions, please do let us know. And here's a link to a really good page on detoxing suggestions:
www.tiredoflyme.com/detox-methods