안녕히 주무세요 /an-nyeong-hi ju-mu-se-yo/ Good night
This is the most formal way to say Goodnight in Korean.안녕히 means ‘peacefully’ and 주무세요, is the formal version of 자다 (to sleep)
굿밤 /good bam/ Good night
This is a slang ,a Konglish sentence, where we combine ‘Good’+ ‘bam'(night in Korean)
잘 자요 /jal-ja-yo/ Sleep well
You can use this expression to wish them to sleep well to somebody. This expression sounds sweet and commonly used to people that you really care about. You can remove -요 for informal (to friends)
좋은 꿈 꿔요 /joh-eun kkum kwo-yo/ Sweet dreams
좋은 means good and 꿈 means dream. This expression means something like ‘dream some good dreams’. Use it to someone you have the same age or rank.
너 먼저 자 /neo meon-jeo ja/ You sleep first
This is a perfect expression saying to someone that you’ll sleep after they first fell asleep. You can only say this if you are really close or dating that someone.
언제 잘꺼야? /eon-je jal-kkeo-ya/ What time will you sleep?
Again this is informal, you can add -요 for a more formal way to your friends
잠이안와 /jam-i an-wa/ I can’t sleep.
This expression is commonly used. But it literally means ‘the sleep is not coming’
늦잠잤어 /neut-jam-ja-sseo/ I overslept.
You can use it when you wake up literally late. The best time to use this is if you are late for your school or work.
잘 잤어요? /jal ja-sseo-yo/ Did you sleep well?
If you want to ask if they sleep well, use this. You can remove -yo if you are close with the one you are speaking with.