That's kind of what I was thinking - and directly contradicts other claims in these comments that want to attribute it only to the weight loss.
Personally I've cycled through keto a few times. I will say that while it did not line up with my goals sufficiently (you cannot powerlift/bodybuild long term on keto - your body _needs_ exogenous glucose for that) I was way more clear-headed and alert despite being tired all the time (presumably that's more because of the workouts).