At first, I wasn't sure if I was reacting to the medication or if it was an immune response as my immune system started to recognize/react to the virus. I was fortunate that my lymphadenopathy/sore throat started to improve the fist week and this was my sign that the antiviral was doing something good. Next came improvements in brain fog, but I think it took 4-6 months before all "side effects" cleared. Now I don't react to valacyclovir anymore than to a glass of water. So in my case, all the initial side effects were due to the immune system recognizing the EBV.
I have had ups and downs, but overall, I am better than 3 years ago. When I started improving with valacyclovir, I thought I had found the answer, but my improvement plateaued. The valacyclovir helped most with brain fog and flu symptoms. In addition to addressing EBV, I'm now also addressing a Candida krusei overgrowth with nystatin, and a mold exposure (the door of my fridge had a leak and was filled with stachybotrys).
I've tested for lots of stealth infections and toxic exposures and I've been fortunate to be able to identify three of my "hits" (EBV, candida, stachybotrys) and that there are actionable ways to address them. I'm still limited in what I can do, rely on medications, and have to wear full leg and abdominal compression to get out of bed.... but I have gone from moderate to mild. I am able to hold a job (from home), leave the house, and spend limited time with friends, for which I am very grateful.