What is the tweaking phase in Methamphetamine binge use?

I've been told that methampethamine addicts who binge use the drug can go on a tweaking stage and its dangerous. Can some explain this "tweaking phase" or provide a nice reference site that discusses this.

: http://alcoholdrugstreatment.info/what-is-the-tweaking-phase-in-methamphetamine-binge-use