I'm halfway through a flat move, the first in two years, and I'm absolutely exhausted. I can't quite believe how much stuff I've managed to collect. We've thrown a good portion of it away, but still, there's tons.
And I've done my back in. Ironically, by carrying a box of cardboard boxes (a 'home moving pack') back from Argos. It was 10K and an awkward shape and almost killed me.