Hey Turtle, I can relate. Dipping was a big part of my college and grad school experience. I'm sad to say that not only did I dip all the way through school, I actually picked it back up again when i went back to grad school. It was so much a part of me that I couldn't get by without it. Its a sad state of affairs when you can't fuction properly without an addictive substance.
Truth be told, its gunna suck. You'll have a hard time focusing. But would you rather have a hard time focusing for a little while or continue being a slave to a can that will kill you.
You can do it. Just toss out the can, suck it up and quit. You've got a lot of support from the members of this site and you're quit group. You can do it, you just gotta take the first step.