You're like a dream.
sei CO-me un SO-gno — stress on 'co-' and 'so-'. 'Sogno' is two syllables: SO-gno.
A poetic and deeply Italian compliment — comparing someone to a dream is one of the most romantic things you can say.
'Sei come un sogno' = you are like a dream. Simple but powerful. 'Sogno' = dream. Italian poetry and song are full of dream comparisons — using one naturally places the speaker within a long tradition of Italian romantic expression.
Ho paura di svegliarmi.
I'm afraid of waking up.
Perfect follow-up — implies the situation feels like a dream you don't want to end
Sembri uscito/a dai miei pensieri.
You seem to have stepped out of my thoughts.
Beautiful — implies you had imagined someone like this before they appeared
Non pensavo esistessero persone come te.
I didn't think people like you existed.
Wonderment — the person is almost too good to be real
Italy has a rich oneiric (dream-related) tradition in poetry and song — from Leopardi to the lyrics of 1960s cantautori. Comparing someone to a dream is invoking this entire tradition. It says the person is beautiful enough to have been imagined before being encountered.