When Luna collapsed the previous position was ranked 8th, ranking and marketcap never guaranteed safe, always alert is the best thing so we don't regret it, if there is a coin that we hold and drop more than 5% a day then always observe and immediately take decisions or sell before losing bigger.
Agree CMC is only a reference to see the trading performance of a coin not to determine whether they are good and safe as an option, even almost all altcoins are not safe to choose because all are at risk, developers may dumb away the coins they hold or leave the project without you being clear about the continuation of its development
But a 5% drop in a day is still quite reasonable in my opinion which is dangerous if the decline reaches tens of percent in a day it's a bad sign and maybe the holder is a little too late to sell it.
Regarding Op's question, it's quite strange because even altcoins are hard to predict in the short term let alone the long term, and the question was made in 2021 where if he realized it would be a good time to sell the altcoins he held