Your body probably got accustomed to the routine chelation and developed supportive processes to chelate the mercury. Found without it's aide from ALA and DMSA, it could not cope with the situation adequately.
Similar thing has happened with me and the liver flush- at the 4 or 5 week mark my system automatically squirts out bile. Pretty intelligent system- the body.
Try randomizing your schedule a bit. You are in the dump phase so I wouldn't completely cease chelation for very long