Anyone with understanding of Bitcoin and how volatility works would not panic when the price drops. Those who lack the knowledge of the basics and are only into it for a quick profit would.
What kind of Bitcoin knowledge claims it will only go up in price? There are plenty of factors that have the potential of seriously crippling Bitcoin price for a very long time.
Panic is an emotional state and emotions are not something that should affect trade decisions, but the same can be said about holding forever spproach. Selling when the price starts do drop is often a wise move.