I had moderate fatigue and hair loss and ferritin level below 20. (To me, the fatigue was debilitating, but technically not "severe" as I was still able to physically get out of bed and drag myself to work at a desk job.) With ferritin levels below 20, I used IronSorb for about a year with no improvement. I was switched to ferrous sulfate (standard cheap drugstore tablets) and my levels finally began to rise. However, a year and half after using ferrous sulfate at 3-4 tablets (65mg each) a day (sometimes I can't tolerate 4 tabs due to headache), my ferritin is still only 40.
The fatigue improved by half within several weeks after starting ferrous sulfate and the hair shedding is somewhat improved, though it is still higher than normal.
I wish I knew what I could do to increase my ferritin to the recommended levels of 70+ to stop the hair shedding, but I am already taking the maximum amount of iron I can tolerate without headaches.