For the first 2-3 weeks my sleep had improved overnight, but I still occasionally had nap-attacks where I just *had* to have a sleep after work as I was knackered.
I had one yesterday for the first time in aaaaaaaaaaaaaaages, but I had had a very busy weekend at work and hadn't slept well because of it, so I was catching up. I just go with it and feel better for having a snooze, but I'm lucky as no children to mind!
Once your body settles in to the new nutritional regime it does get better.