Is this common? I do get altitude sickness at Breckenridge altitude (near 10K), but did not expect it on the AT. Yet on my section hike this weekend (Clingman's to Fontana over 2 days) I had my worst case ever: headache, lack of appetite, decreased hiking ability (especially on downhills), fever, uncontrolled shivering on stopping (of course it was cold...), chills, and even some chest tightness. I had lesser cases of the same on Shenandoah sections, but had attributed that to overexertion.
I have ideas on how to treat it (e.g., ease into hiking, Vitamin I, hydration, food, maybe even Diamox), just seeing if this is common among "weekend warrior" section hikers.