I think you will find that watching someone else play is worse because when playing the FPS yourself you know which direction the view is going to move so your eyes can pre-empt your screen view (proactive) whereas watching someone else play is reactive. That is what I find anyway.

Having said that, I have been playing Skyrim for a few hours before bedtime lately, and I often still feel like I am moving after I lie down. That rolling motion after getting hit with an arrow really affects me, probably because it is game generated and therefore I can't pre-empt it.