Hi Michelle - it can be just like kicking a drug addiction, don't underestimate what a powerful hold sugar can have on you! I think it's just as potentially addictive as any Class A drug.
I think there is a definite period of physical withdrawal when you decide to cut out the junk (chocolate, crisps, fast food etc.), but worse than that is the emotional dependency that causes you to start to mourn the loss of your food crutches before you even start to lose weight! So good on you for making the actual resolution to kick the habit once and for all - a lot of people don't even get that far.
You might find you have a few headaches and feel a bit strange for the first couple of days while you're still craving sugar, but it *does* dissipate very quickly and the nice thing is that your palate starts to refashion itself - you can taste the natural sweetness in lovely things like fruit and vegetables, and you enjoy eating a hell of a lot more!
I think it really does help if you approach this change in your life not as a 'diet,' but as a long term adjustment of your relationship with food and your relationship with your body. If you can make that step of accepting that healthy eating is for life and resolve that you're never going to go back to the old habits that made you miserable, then I think you take a lot of the pressure off yourself, because you stop thinking in terms of short term goals and boundaries, and you stop expecting lightning quick results. I think there's an added benefit in that the more steadily and healthily you take the weight off, the easier it is to get into lifelong good habits that you'll continue when you get to your goal weight.
You can do it, trust me! You don't need the junk, it's just holding you back and weighing you down, emotionally and physically. It might be quite cathartic to get a big old bin liner and go clear all the lousy food out of the house. If it's not there, it's not tempting you in those important first days.
The very best of luck to you - keep posting here and sounding off if you feel like it. Sometimes it helps just to share!