o the fact that I've recently finished a big, stressful project and felt I had nothing urgent to do any more,
o a rather variable diet over the past couple of days, or
o not getting quite enough sleep the night before,
the overall effect was better explained by the fact that I was ill. I have therefore disappeared home taking my sickness with me. I feel as if I should feel somewhat guilty about this, but generally don't have the energy to do so. I think that that suggests I was probably right to take the time off.