crash diet

All my friends know that I posted several times on my see-saw weightloss performance. It frustrates and discourages me. Well, I need to lose about 20 lbs, so my plan is to crash diet, just to meet my weightloss goal, than I will go back to my "healthy lifestyle".
I know what to do through WW and MFP, to maintain a weight, but I figure I need to get to the "magic number" first. I am an "all-or-nothing" person, and the reason why it's taking me a year and a half just to lose 40 lbs, is because some weeks I'm all for it, other weeks, I could care less. I'm going to drastically cut my calories for the next couple of weeks, and see how it goes. I know intense dieting is not good, but I believe the main ingredient for losing weight is doing what works for you. Conventionally methods for me isn't working so I'm going to try this.