Why does blocking the parasympathetic nervous system stimulates the sympathetic nervous system?

Why does blocking the parasympathetic nervous system stimulates the sympathetic nervous system?
1. Give an example of each classification of cardiovascular system drugs and list 1-2 important key nursing actions/teaching/monitoring/assessment while the patient is on the drug.

Adrenergic drugs

Adrenergic inhibitors/blockers

Beta-adrenergic blockers

Vasodilators

Cholinergic drugs

Anti-cholinergic drugs

2. Why does blocking the parasympathetic nervous system stimulates the sympathetic nervous system?