I checked google for peer reviewed studies of increased toxins or metals in urine after massages but did not find any. There are certainly plenty of articles that say this is bunk. What isn't bunk is that deep tissue massages actually bruises the muscles and releases material into the bloodstream that is toxic, which is why many feel worse after a massage.
Keep getting massages but keep the pressure unpainful. You also might try deep tissue infrared therapy. That helped with a back injury