During strong uptrends, the best practice is to buy on significant dips as profits are produced when the price quickly rebounds from oversold conditions. This appears to be what happened on April 18 as traders jumped at the opportunity to buy Bitcoin and altcoins at lower levels.
However, no market can keep going up in a straight line and periodic corrections and phases of consolidation are needed as they drive away the speculators who only jump in and use high leverage when they sense an opportunity to get rich quickly.