Final answer:
Hold the medication if the postpartal woman complains of headache and dizziness because Methergine can cause vasoconstriction and increased blood pressure.
Step-by-step explanation:
In this scenario, administering Methylergonovine (Methergine) 0.2 mg to a postpartal woman with uterine subinvolution, you would hold the medication if the woman complains of headache and dizziness. The reason for this is that Methergine can cause vasoconstriction, and headache and dizziness are signs of increased blood pressure. Holding the medication in this case would be important to prevent any potential complications.