Dear stellatj,
Both pravachol and zocor belong to a family of medications called 'statins'. These drugs are very good at lowering cholesterol but different drugs have different dosage levels. Therefore 20 mg of pravachol may have the same effect as 10 mg of Zocor. There are not really any warning signs for too low cholesterol. I would recommend a repeat level check in about 6 months time.
Ray