Hey all - thanks very much for your replies, I really appreciate the time taken and support given.
@xrodolfox
Caloric intake - definitely something to consider. My diet is higher GI than is optimal and despite planning a decent breakfast/lunch and snacks on Saturday I had a really horrid sugar crash in the afternoon about 4pm (shaky, sweating, the lot) which is something I don't get that often now.
I am attempting to lose some excess weight though no one could accuse me of skimping on my food...its possible the balance isn't quite right, and the sugar crash was deeply unpleasant!
@Gastroplodder
thanks for the well timed reminder to avoid going into crazy over-exercise too! I am keenly aware of a strong habit to over do anything and everything that makes me feel better. I certainly have gotten over-obsessed with exercise in the past, and I totally identify with the sneaky desire to just keep going and never have to deal with the come down!
As for the three-day week - bah and humbug! Worst thing is I'm half self-employed and do love my job, but it still gets in the way

@JS
I think I need more amusing PJs! Thanks for your experiences, feels very familiar!
For anyone reading and concerned, I do have an excellent therapist that I use as and when needed, and am now taking St Johns Wort for 6 months on a trial basis. I've previously tried almost all the available medications and while I had some benefit when younger in the past three years have found nothing to make enough difference when balanced against the increasing side effects.
On the plus side, the two-three days of yack is pushing me to re-evaluate my work/life/exercise balance. I'm hoping to go fully self-employed later this year - must keep sane till then though!
Thanks again folks
Mog
The greatness of a nation and its moral progress can be judged by the way its animals are treated.
Mahatma Gandhi