I guess it's possible it could be some sort of low grade infection, as I've not been feeling well recently, though it's been kind of on and off. (perfecthealthdiet.com)
For instance, low grade infections, toxic metals and chemicals, food sensitivities, etc.. (robdaquila.com)
Both were hot after the master's 32 - year - old blood, and it didn't help that Moses had been fighting off a low - grade infection for 10 days. (si.com)