Effects of Magensium

I have taken magnesium at night after dinner (200 mg of magnesium from vitabiotics brand; They have not mentioned what form of magnesium is present in the tablet. They just mentioned only elemental magnesium 200 mg) for last few days and found my muscle pain and hand pain decreased substantially. However, the focus and concentration decreased very much with magnesium consumption at night. So, I have changed the timing to morning after breakfast and observing.