Any heavy metal chelation would be very hard on the adrenals if you have adrenal fatigue.
Not only that DMSA binds to heavy metals and excretes through the urine and that means the kidneys. So if you have elevated kidney test results it will put them under immense pressure, Unlike your liver if your kidneys get damaged they can't regenerate themself.
Even though 3 days doesn't seem like a lot. To someone sensitive it could be.