I'm taking chantix too and I think I'm drosy/foggy during the day because I'm having trouble getting to sleep at night. I can be tired all day and then when I lay down in bed I can't fall asleep. It's weird. But even today when I slept for over 9 hours last night (!) I was groggy when I got up. I think some of it might have to do with the fact that nicotine is a stimulant, but if you just started the meds you are probably smoking for another 7 days so that wouldn't apply.
But we all react differently to the same drugs, so who knows? I too had a vivid dream right away, but I think mine was the second night. When is your quit date? Keep us posted! I posted here on my quit date and there is lots of support out there for you!