It is correct that on trading there is nothing loss until it is panic sell but if the price drop too much and it goes to to below and don't recover then it remains loss though it is not sold. Also there is no way to recover for example ,if we consider about the luna than it will be clear about the loss without selling. Though the value is not 0 but it is near 0 and there is no chance for recover.
Until the coin is sold, it should still not be considered to be a total loss but can only be said to be a reduction in portfolio value. If we are to talk about the Luna crash, I will say it's a complete disaster. Not only do most of them lose their investment, but they were also affected mentally, which will be hard for some to recover from. The coin is in its dying stage; no matter what's keeping it alive for now, its chance of recovery is very low.
If we are talking about not being in a loss in trading not until when you panic sell them we should also consider if the trader is trading in features or spot. From my knowledge it's typically in spot trading that even if the coin you trading falls below and your funds liquidated you can still be in profit should the coin rise again provided you still maintain your trading position. But not same with features, once your funds are liquidated that's the end of your trade, you automatically in a loss non-recoverable. But above all, what's worse is a coin crash like in the case of LUNA.