Illness resulting in (at this point in time, at least) not being able to exercise at all.
Viral/stress related. Having recovered from symptoms after 10 days, continued to feel weak for 3 weeks after so did no training. Pleasantly suprised to find my fitness level had not declined much. Also delighted that I'll be able to finish off the season OK, having missed 3 weekends of races, including the British Championships and CompassSport Cup qualifiers.
7 days off work, 4 races missed.