Burning sensations and bad moods

Today I am feeling cantankerous.  Curmudgeonly, even.  Watch out.

Why?  No reason, of course.  Well, there is a contributing factor (I am fairly certain), but it is purely biological and cannot be helped.  Nothing short of a beach chair and a pina colada on a secluded beach somewhere is going to make it go away. 

So let's just move on from there, shall we? 

Last night after class was over and I wandered zombie-like back to my car to drive home at 9 p.m., an interesting thought popped into my head.  This is my third fall semester as a grad student.  While the courses I have taken for my fall semesters as well as the particular days I have scheduled classes has changed, one strange phenomenon has remained constant.

Actually, this phenomenon is not likely directly related to school itself.  At least I do not think so.  It is related to my weak physical structure.

Every time I have an evening class that takes place after a full day of working in the office, around 8 p.m., my eyes give up their will to live.  Yes, they get droopy and it becomes hard to keep them open, but this is not the strange thing.  They do not just droop, they start on fire.  In order to put out this fire, they begin to water.  They itch.  All I want is to shut my eyes in a dark room and go to sleep.

Unfortunately, at 8 p.m., I usually still have an hour left of class, so this is not an option.  The only relief comes from removing my glasses for about 15 minutes.  It doesn't really help the fact that my brain is shutting down from exhaustion, but at least I can keep my eyes open without looking like I have been crying all day.

My first guess as to the cause of this drama would be allergies.  After all, I tend to have a similar reaction when trapped in rooms with cigarette smoke or when my car's air circulation system brings in outside air during the fall or spring.  Yeah, that's right.  This sometimes happens to me while driving.

But if this is so, why does it only happen around 8?  Why not all day?  Or at least from the beginning of class?

My next theory is that it has something to do with computer screens.  I sit in front of one all day at work, followed by three hours in front of one for school.  If this is the case, it may explain why the removal of my glasses causes some relief.  It allows my eyes to fall out of focus and not spend as much time looking at the glow of the screen. 

My final theory is that my school is haunted.  Not by evil ghosts, but by mischievous ones, sort of like Peeves from Hogwarts.  Every night around 8 p.m., this silly little spectre sneaks in and sprays dust or pollen into my eyes beneath my glasses.  The reason that the removal of my glasses helps is that it allows the dust or pollen to escape. 

Which theory sounds the most plausible?