You only lose what you wanted to have but couldn't not what you might have had.
To clarify, there is no "perceived loss" in my opinion but only loss or gain. For example if you want to accumulate more fiat then if you bought bitcoin at $30k and then sold it at $40k and then price goes to $50k then you have not lost anything because you have your $40k which is now $10k above the initial $ amount you had.
Conversely if you want to accumulate more bitcoin and in the same scenario above you have actually lost a lot because if you buy back you won't get the 1 bitcoin that you initially had but only get 0.8 bitcoin.
When stablecoins were first introduced, I did not read about them nor understand them,
There really isn't anything special about stablecoins. They are centralized altcoins that promise you to have a stable price and to not vanish suddenly but at the same time they can very well disappear at any moment or have a price that is lower or higher than what they promised. They can also lock your account and take your stablecoins.