Re-experiencing the effects of drugs while they are stirred up in the body is definitely what happens.
This cleanse is quite powerful and it wouldn't surprise me that it actually dislodges drug residues.
Residues from drugs get lodged in the fat tissues of the body and don't come out easily. Which is probably the reason for the high relapse rate of people completing drug rehab programs.
The drugs aren't getting cleaned out causing the person to still crave more drugs.
The only program that I know of that has a high success rate and actually gets the drugs out is called "The Purification Program".
Apparently the Master-Cleanse may have some success with that as well.