Answers:
Nervousness is nil more than Sympathetic Nervous System stimulation. The same entry that happen when you are excited.
The body releases catecholamines (dopamine, norepinephrine and epinephrine (A.K.A. Adrenaline)) that increases the heart rate which sometimes cause a premature ventricular contraction (PVC) or palpitation within adjectives language. (Completely normal)