It can go either way... hyperactive insomnia to foggy sleepy dullness. It's all down to the chemicals in your brain going "What? No smoking? HUH???" and basically not being able to coordinate in any accustomed fashion. It's withdrawal, essentially, we just don't feel a lot or most of it, thanks to vaping.
For most, I think that's over in, what, about 3-4 wks? If it persists, especially the foggy-unable to focus thing, you might try some WTA; it can help a lot, but it's a good idea to see if you really need it, because it's a good bit more expensive than regular nicotine or ejuice.
Andria