Well I took an extra rest day this weekend as I have been feeling very tired and running on empty (forgive the pun). Anyway set off today with a sniffly nose and a little bit of a sore throat, feeling a tad apprehensive. It was a much better day, I had more energy, travelled further and in a slightly quicker time (which is still snailpace). Maybe I've been harbouring some nasty virusy thing and am now getting over it. I actually felt good at the end of this run rather than drained.
Anyway the extra rest day helped so much that I will be sneaking some more in if needs be.