Man, I feel you. I am recently through the fog and I promise, it does get better! You got this. The best advice out there is just to embrace it. Make it an experience that you owned.
My fog was just like you described - can't concentrate - especially at work. It was damn near impossible just to write an e-mail correctly. Don't worry, it will pass. You will be through it in no time.
Another pleasant part of the fog is sleeplessness. I still fight a little bit with this even after 40 days quit. Mine was so acute, I woke up at 2:00 and 4:00 am, every day, on the dot... you can set your watch by it. My mind was messing with me all the time.
But, somewhere as the days added up, the fog cleared up. The cravings really subsided and life got much better.
You got this... trust me, if I can make it through the fog - you can to. Just embrace the ride - don't forget how much it sucks and remember there are a bunch of people walking in your shoes right now. There are a bunch more who have been there.
This site has really been a big help to me. Stay on it - YOU GOT THIS NAILED MAN.