Oh, I know, but I'm always like this (as in, not just when doing W30), so I'm hoping that someone else who dealt with low energy pre-W30 will tell me that completing it made them feel so much better, as encouragement. :-)
So, I didn't have pre-W30 super low energy, but during the beginning of W30 I was going to bed as soon as my kids were in bed on the regular. Like, 8pm. And I'd sleep like a rock until they woke me up again at 6:30-7. It was hard b/c I felt like all I was doing was cooking, working, dealing with children, and sleeping. Zero time for me or my husband.
However, it did get significantly better and I have found (post-w30, but sticking to what I learned) that I have more energy throughout the day (no 3pm slump)
Anyone who has ever asked me about the whole30 I have the same response. The first week is hell. It seems so easy. Meat, veggies, fat. So easy...
Until you just want to eat all the things and you are exhausted, and a little (or a lot),of a bitch on days 4 and 5 with a hair trigger temper. All the while you start just getting more tired. By day 5 you just want to pull the blankets over your head and be done.
But! But I promise by week two you even out and food becomes almost a chore and you have remind yourself and sometimes even force yourself to eat.
And tiger blood hits. And suddenly you start having the most level emotions ever and days begin to become crystal clear and you have a memory again. And patience again. And the good clean living you didn't think you could do. And you are doing it. And finally sleeping through the night. Solidly.
Stick it out. Base nothing at all on week one. Just survive it and eat as much as you want (as long as its compliant). You won't feel like this forever. Or even for another week.