I had a lot of problems with a constant sinus infections after catching a weird respiratory virus that led to CFS. I have no sinus pain, fortunately, but I find that as the severity of my sinus infection increases, I experience horrible anxiety levels (generalized anxiety disorder symptoms). I suspected that these anxiety states are actually CAUSED by the sinus inflammation.
This has turned out to be true: as soon as I eliminated my sinus inflammation (with dietary changes and certain supplements - see later), the anxiety states went away too. So I think sinusitis can actually be a major cause of anxiety states (and perhaps other CFS symptoms too).
In fact, it has been observed that people with CFS, who have sinus surgery to fix their sinusitis, sometimes find that their CFS symptoms greatly improve afterwards. So I am guessing that an ongoing infection in the mucous membranes of the sinuses can affect, or perhaps even spill over into, the brain or hypothalamus (located right next to the sinus cavities), and exacerbate the symptoms of CFS.
The viruses that are thought to cause CFS/ME (Epstein-Barr virus, HHV-6, parvovirus B19, Enterovirus) principally replicate in the mucous membranes, be it the lining of the intestines, stomach, throat, or sinuses, so it makes sense that there is some ongoing sinus inflammation in CFS patients with these viruses, just as there usually is ongoing gut infections - these viruses can inhabit the entire respiratory and gastrointestinal tract, from mouth/nose to anus.
Anyway, I found that the best thing to help clear up the constant sinus inflammation is firstly eliminating dairy products entirely from your diet. No milk, cheese, butter, cream, whey, yogurt. These contain lactose and casein, which promote mucus formation in the sinuses.
Then in addition you may need to add several herbal supplements to your daily regimen that are good for clearing sinus infections. I found that good doses of reishi, echinacea, propolis, and MSM worked well. But there are many supplements that also can help clear sinusitis: cat's claw, cinder vinegar, colostrum, cinnamon seeds, ginger, ginkgo biloa, guaifenesin, horseradish, myrrh, bromelain, oregano, bilberry, goji berries, Pelargonium sidoides, Terminalia chebula, N-acetyl-cysteine, pantothenic acid, and high dose vitamin A.