I have Fibromyalgia -Vitamin D3 supplementation cleared the constant muscle pain (for the most part). I did high levels for 3 weeks & was pain free. I knocked the dose down to 2000iu's a day & a week later the pain was back. After restarting high levels, the pain is managed again after 3 days.
I personally did 35,000iu per day for 2 months trying to refill my stores. It is highly recommended that vit.D levels are tested but my research shows toxicity only at outrageous, long term levels.
I was concerned with overdoing it til I watched one of Dr.Mercola's video's on Vit.D & he cautioned not to overdo but said if you were ill that 200,000iu for 3 days is fine.
I originally did B12 injections daily for a couple of years & then I tried guaifenesin (Dr.St.Amand's protocol) for 10 years but discovered vit.D3 supplementation only recently & that has worked better than anything else!