My head throbs, my eyes itch and I'm woozy with fatigue. The floor is lurching and voices sound distant. Yes, I've been teaching all day.
I can't blame the kids, though. They're little darlings most of the time. Nor is my workload wearing me down. In Canada, there are no Ofsted inspectors or league tables to make life miserable. The cause of my symptoms is much less obvious - it's my classroom.
It's new, too. Two years ago, my school bulldozed its ramshackle portables and built four "learning centres". They're nothing special: the usual breeze-block walls and blue plastic chairs, but at least the ceilings aren't mouldy. And, unlike older rooms, they do not harbour 30 years' worth of dust, dead skin and bubble gum. Really, I ought to be happy.
But I'm not, and the reason is simple: like my students, I'm the victim of bad design.
Take my classroom's lighting. There are 32 overhead fluorescent tubes, and they're all either on or off. If they're off, I teach in a grey semi-darkness because the badly placed window lets in so little natural light. If they're on, they're ridiculously bright and over-stimulating.
Sometimes I think I'm oversensitive, but then I consider all the research that's ignored by penny-pinching school builders the world over. Fluorescent lighting has been found to cause headaches, tiredness, eye strain, irritability, malaise, poor judgment and difficulty concentrating. Production of hormones is also affected - perfect when you teach adolescents. But here's the real kicker: flickering fluorescent lights have been linked to hyperactivity.
The other big problem is air quality. First of all, the nitwit who designed my classroom ignored basic science. Despite the fact that hot air rises, he or she put the heating ducts in the ceiling. Obviously, it's so that my students will spend all winter saying "It's freezing, Mr Woolley!" while the air just above their heads is as hot as Arizona in July.
The result? A maxed-out thermostat and poor air circulation. By the end of the day, my room has the same dry, itchy, groggy atmosphere as a charter plane after a long-haul flight.
A recent study from Cornell University found that even a small build-up of carbon dioxide, the result of too much breathing in a confined space, can lead to sick- building syndrome - everything from headaches and dizziness to irritability and memory loss. Throw in the students' post-PE body odour and cheap deodorant, and the result is a heady cocktail.
According to Rena Upitis, a professor at Queen's University in Ontario, classrooms like my white-walled box classroom would be horribly misconceived even if they had perfect lighting and air circulation.
In her paper, Tackling the Crime of School Design, she writes: "Overly durable and hard architecture tells children this is what they have to look forward to - life in cold and deadly buildings that will repress their bodies, minds and spirits."
We teachers have to do something about our buildings. And I would, but I need a lie down.