I've given it a few days to see if it is true, but it definitely is. My mojo has returned.
I've had about 2 months of really struggling with my commute. My average speed, which used to hover around 27kph, had dropped to 23kph. This added 10-15 minutes to my commute.
Since my 'sleepy-exhaustion' 3 days last week, I feel like a new person. 27kph on the flat feels like dawdling, and I even kept up with clifton cycles chain gang for a bit, at 40kph (I had turn off just before I was going to open up and humiliate them