In fiat terms, yes. The loss is only realised once you convert the Bitcoin back to fiat.
The reason it is "unrealised" until that point, is that you could instead simply hold until/if the price of Bitcoin (priced in fiat) rises past the level you bought it at, and still sell at a profit (in real terms if you account for inflation, or in nominal terms if you don't).
Then that would be a realised profit.
Hence the distinction between unrealised and realised.
The reason it is "unrealised" until that point, is that you could instead simply hold until/if the price of Bitcoin (priced in fiat) rises past the level you bought it at, and still sell at a profit (in real terms if you account for inflation, or in nominal terms if you don't).
Then that would be a realised profit.
Hence the distinction between unrealised and realised.