Listener fatigue: what does it really mean?

Okay, so I used to think that listener fatigue meant that your ears just kind of got tired from listening to speakers that were overly bright. I don't have a good understanding of the make up of an ear, but I believe there are muscles in an ear that, I guess, expand and contract while we listen to music and I figured that's what it meant to have listener fatigue. Now, I'm thinking that listener fatigue is maybe more than your ears just getting tired but actually, your whole body getting tired and feeling drained. I experienced this time and time again listening to my paradigm studio's. They are somewhat bright and provide quite a bit of detail in my oppinion, so I'm wondering if, since there was such a great amount of detail coming through, that it was physically draining because I'm sitting there analyzing everything that's coming through the speakers. I would wake up and first thing in the morning, grab a cup of coffee and start listening to music (my daily routine) and 20-30 minutes later start nodding off and I couldn't figure out what was going on. I've been sitting here this morning listening to my new vandersteen's for two hours and can't get enough. I feel like I could listen all day and that I'm almost energized from listening vs. drained.

Soooo, what are your oppinions about what listener fatigue is and why it's caused?