SarahAnne wrote: By about the 4th to 7th day, I become very sluggish.
Sounds like "keto flu." It really takes a couple of weeks to adapt and get your own ketone system out of mothballs. The latest suggestions talk about making sure you consume extra sodium, potassium and magnesium salts, especially during this conversion period to mitigate the "flu". Ketone salts might also be useful as would give your brain something to feed on while going through conversion.
I have an E3/4 friend that ordered some Keto Force salts. He took some and went to the gym. Said he felt like he was on rocket fuel. Normally was "done" at the end of an hour of lifting and he went on for two on the salts.
Though I don't work on staying in ketosis all the time, I have been keto-adapted for ~4.5 years. For my athletic activities, this has been very useful. Some things I've noticed:
a) don't need as much water to stay hydrated at altitude while playing
b) almost never ever breathe hard, even playing at 12 or 13,000' (I live at 5,500' elevation)
c) don't run out of energy - I never do endurance cardio for training (only super slow lifting to failure), yet can keep up with my cardio fiend friends during our activities
d) eating 1 or 2x/day is no big deal, nor is fasting for longer periods of time