I like the interpretation that Lily, believing it was a dream, asks Fjord to "not wake up" as in leaving the nice dream scented of blooming flowers where there is nothing that could harm them. However, as it is actually not a dream, Fjord might have interpreted "don't wake up" as not losing track of his dreams. I believe Fjord has established his life similar to that of a nightmare, and as such, it was evident that he had goals or dreams to accomplish like the ruin of his mother's rule or at least the escape of it.
Because of what happened to Lily, he might have thought of giving up. His goals were just merely dreams he can't accomplish because someone he wished to protect the most had gotten hurt (or almost killed). Not waking up is like not giving up... I guess?
Ch 66
Why did MC say "Don't wake up" to Fjord? Was it a mistranslation or am I missing something?