classic equity trading history shows that buying falling assets is a very bad idea. For crypto alt coins i would say it is even worse idea. Even if coin has any fundamental reason to gain in value (highly doubt about that) it can take ages to recover.
the golden rule of technical analysis is buying only if price action is uptrending and showing higher highs and higher lows.

i think it is a bad idea to buy explosive rallies as well. if you are late in the action it is better to wait for correction and only if price starts to uptrend again buy it at that point.