अपनी धुन में

Not necessarily. It's usually neutral or even slightly positive, implying the person is self-sufficient or focused. However, if they miss something important because of it, it can be a mild criticism.

Yes! You can say 'मैं अपनी धुन में था' (I was in my own world) as an excuse for not noticing something.

'Duniya' (world) is more common in modern speech, while 'Dhun' (tune) sounds more poetic and traditional.

No, despite the word 'Dhun' meaning tune, it applies to any activity—reading, walking, thinking, or even just sitting quietly.

It's better suited for casual or semi-formal conversations. In a very formal setting, use 'एकाग्र' (concentrated) or 'मग्न' (absorbed).

The phrase itself is static. You conjugate the verb that follows it, like 'rehna' (to stay) or 'khona' (to be lost).

Yes, 'वे अपनी-अपनी धुन में थे' (They were each in their own worlds). Note the repetition of 'apni-apni'.

Yes, 'अपनी मस्ती में' (In one's own fun/intoxication) is a more casual, slangy version.

Usually, yes. It implies a state of contentment or at least a lack of stress about the outside world.

It's a bit too poetic for that. For drunkenness, 'नशे में' is better, though 'अपनी धुन में' could be used euphemistically.

There isn't a single idiom, but 'दुनिया की परवाह करना' (worrying about the world) or 'चौकन्ना रहना' (staying alert) are opposite states.

Extremely! Many songs use this to describe the feeling of being in love or being a free spirit.

Yes, you could say a cat is 'apni dhun mein' when it's playing with a ball of yarn.

It's used by everyone, but older people might use it more to describe a 'dreamy' younger generation.