Two thoughts... If it was a DLP (unlikely these days) there is an issue called rainbow effect that can cause eye strain and headaches. The second thought is brightness. Every HDTV I've ever seen has come with the brightness set far too high, which can certainly cause eye strain. Essentially they're all set for the conditions of a showroom (bright flourescent lights and such) and when folks get them home they forget that calibration is a must.
