Thanks Ladies, all great suggestions.
With DD I used to duck off to the car for a nap at lunchtime, I might need to start that up again.

I will have to get myself some nuts or something to munch on, maybe that will help.
I'm already drinking by the bucket load!

Walking is pretty much out, as the SPD makes that a mammoth effort at the best of times. I might just try moving desks to near the window each arvo, a bit of extra natural light couldn't hurt I'm sure.

Again, thanks for all your help.