Learn Hardcore Norwegian: Jeg sovner på den myke sofaen etter en lang samtale. - I fall asleep on the soft sofa after a long conversation.

Sovner is the present tense of sovne, which means to fall asleep.
Sover comes from sove, which means to sleep.
So jeg sovner means I fall asleep, while jeg sover means I sleep.

Why does the sentence use på den myke sofaen? What does på mean here?

In Norwegian, på is used with surfaces and furniture (chairs, tables, sofas) – literally “on” or “upon.”
For enclosed spaces (rooms, cars) you use i.
Therefore på den myke sofaen means on the soft sofa.

Why is it den myke sofaen instead of just myke sofaen?

When an adjective describes a definite noun in Norwegian, you need:
• a demonstrative or article (den for common gender)
• the adjective in its weak form (ending in -e)
• the noun in its definite form (suffix -en)
Hence den myke sofaen = the soft sofa.
Without den, you would use the indefinite form en myk sofa = a soft sofa.

Why does lang have no ending in en lang samtale, but myk becomes myke in den myke sofaen?

Adjective endings in Norwegian depend on gender, number and definiteness:
• Indefinite singular common gender: no ending (e.g. en lang samtale)
• Indefinite singular neuter: -t (e.g. et lite hus)
• Definite (all genders) and all plurals: -e (e.g. den myke sofaen, de lange samtalene)

Why is sofaen paired with den and not det?

Nouns in Norwegian are either common gender or neuter.
Sofa is common gender, so its demonstrative is den and its definite suffix is -en → den … sofaen.
Det is used with neuter nouns (et hus → det huset).

Could I say på en myk sofa instead? What changes?

Yes. På en myk sofa is the indefinite form meaning on a soft sofa.
In that case:
• You use the indefinite article en
• The adjective has no ending: myk
• The noun has no definite suffix

Why is etter en lang samtale at the end of the sentence? Could I move it?

Norwegian word order after the main verb typically follows place–time. Here på den myke sofaen (place) comes before etter en lang samtale (time).
You can also front the time phrase, but then you must invert subject and verb:
Etter en lang samtale sovner jeg på den myke sofaen.

How do I express I fell asleep (past tense) in Norwegian?

Use the past form of sovne, which is sovnet. For example:
Jeg sovnet på den myke sofaen etter en lang samtale.

How do I say I am about to fall asleep to emphasize the process?

Norwegian does not have a separate progressive tense. You use simple present (jeg sovner) for both “I fall asleep” and “I am falling asleep.” To highlight the ongoing process, use holde på å + infinitive:
Jeg holder på å sovne på den myke sofaen etter en lang samtale.