Well, I'm on day eight. Let's see what I'm going through:
Food: Huge sugar cravings, I've eaten a raft of ice cream last week and my pants are tight. I just let it go because it was the least of my worries. I did go to the gym, and will continue that but today I'm ramping down the sugar intake. Now that I'm on week two my body could do without the sugar bombardment.
Sleep: Sleep is probably the most important thing we need at this point. I have great sleeping habits (go figure) and have slept like a rock all week. Sleep and water, all I want at this point.
Foggy? Hah! I felt clear as the mountain air for the first three days. Now every day I'm getting foggier. It just shows you how impaired we were. I expect to be foggy for weeks, if not months. I know it will clear, and for me it's a hopeful sign that I'm getting better!
So, just like 24hrsAday said, it depends on how long, how much, and also how your body can rebound. It took years to get in this shape, it takes your body months to get realigned.
Keep it up! You'll feel better every day.