Jeg er stadig søvnig om morgenen, hvis jeg går sent i seng.

Both stadig and endnu can sometimes mean still, but they are not always interchangeable.

In this sentence, stadig is the natural choice because it means still / continuing to be in a general sense:

• Jeg er stadig søvnig = I am still sleepy

Endnu often has more of a sense of yet / still up to now, and it is especially common in negatives and questions:

• Jeg er ikke færdig endnu = I’m not finished yet
• Er du her endnu? = Are you still here?

So stadig fits best when describing an ongoing state like being sleepy.

Søvnig means sleepy / drowsy. It suggests that you feel like sleeping.

Træt means tired more generally. You can be træt after work, exercise, or a long day, even if you do not necessarily want to sleep immediately.

So:

• søvnig = sleepy
• træt = tired

In this sentence, søvnig is more precise because the context is about going to bed late and feeling sleepy the next morning.

Om morgenen is the normal way to say in the morning when talking about mornings in general.

• om morgenen = in the morning / in the mornings

By contrast, i morgen means tomorrow, and i morges means this morning.

Examples:

• Jeg drikker kaffe om morgenen = I drink coffee in the morning
• Jeg tager af sted i morgen = I’m leaving tomorrow
• Jeg var træt i morges = I was tired this morning

So in your sentence, om morgenen is correct because it describes a habitual or general time.

The form morgenen is the definite form of morgen:

• en morgen = a morning
• morgenen = the morning

In the expression om morgenen, Danish uses the definite form. This is a very common pattern with times of day:

• om morgenen = in the morning
• om aftenen = in the evening
• om natten = at night

So even though English says in the morning, Danish uses a structure that literally looks more like about/on the morning, with the definite form.

Hvis means if and is used for a condition:

• hvis jeg går sent i seng = if I go to bed late

You usually use hvis when something is conditional, not guaranteed.

Når means when, and it is used when something is expected or happens regularly.

Compare:

• Hvis jeg går sent i seng, er jeg søvnig om morgenen = If I go to bed late, I’m sleepy in the morning
• Når jeg går sent i seng, er jeg søvnig om morgenen = When I go to bed late, I’m sleepy in the morning

Both can work, but the nuance is different:

• hvis = if that happens
• når = whenever that happens / when it happens

Danish often uses the present tense where English also uses the present tense in general truths and conditional sentences.

So:

• hvis jeg går sent i seng literally uses present tense
• English does the same: if I go to bed late

Danish does not have a separate future tense form in the same way many learners expect. It often uses:

• the present tense, or
• forms like vil or skal when needed

Here the sentence describes a general pattern, so the present tense is completely natural.

Yes, gå i seng is a very common fixed expression meaning to go to bed.

Literally:

• gå = go / walk
• i seng = into bed

So the expression is very close to English go to bed, even though Danish uses i where English uses to.

You should learn gå i seng as a whole phrase.

Examples:

• Jeg går i seng nu = I’m going to bed now
• Hun gik sent i seng = She went to bed late

In gå i seng, Danish uses seng without the definite article because it is an idiomatic expression.

• gå i seng = go to bed

This works like several fixed expressions where Danish does not use the article the way English learners might expect.

If you said i sengen, that would usually refer more literally to being in the bed rather than the general action of going to bed.

Compare:

• Jeg går i seng = I’m going to bed
• Jeg ligger i sengen = I’m lying in the bed

So i seng is the standard form in this expression.

Sen is the adjective form meaning late.

When Danish uses an adjective as an adverb, it often adds -t:

• sen = late
• sent = late, used adverbially

Here sent describes the verb phrase går i seng:

• går sent i seng = goes to bed late

The same pattern appears in many other words:

• hurtig → hurtigt
• langsom → langsomt

So sent is the correct adverb form here.

Because hvis introduces a subordinate clause, and subordinate clauses in Danish do not use the main-clause verb-second pattern.

In a normal main clause, Danish usually puts the finite verb in second position:

• Jeg går sent i seng

But after hvis, the clause is subordinate, so the normal order is:

• hvis jeg går sent i seng

Not:

• hvis går jeg sent i seng

This is an important contrast in Danish:

• main clause: often verb second
• subordinate clause: subject before verb

In standard Danish writing, a comma is usually placed before a subordinate clause, including one introduced by hvis.

So:

• Jeg er stadig søvnig om morgenen, hvis jeg går sent i seng.

This comma helps show that the second part is a subordinate clause.

You will see this very often in Danish with words like:

• hvis = if
• fordi = because
• at = that
• når = when

So the comma here is normal and expected.

Yes, absolutely.

You can say:

• Jeg er stadig søvnig om morgenen, hvis jeg går sent i seng.
• Hvis jeg går sent i seng, er jeg stadig søvnig om morgenen.

Both are correct.

But when the hvis-clause comes first, the main clause must have inversion, so it becomes:

• Hvis jeg går sent i seng, er jeg stadig søvnig om morgenen.

Not:

• Hvis jeg går sent i seng, jeg er stadig søvnig om morgenen.

That is a very important Danish word-order rule.

Yes. In this sentence, stadig comes after the verb er, which is a very normal position for an adverb like this in a main clause:

• Jeg er stadig søvnig

This is similar to how many common adverbs are placed after the finite verb:

• Jeg er altid træt om mandagen
• Han kommer ofte for sent

So the position of stadig here is natural and standard.

The sentence is already natural, but in everyday speech some people might choose slightly simpler or more conversational alternatives, such as:

• Jeg er stadig træt om morgenen, hvis jeg går sent i seng.
• Når jeg går sent i seng, er jeg stadig søvnig om morgenen.

The original sentence is perfectly good Danish. A speaker might just choose træt instead of søvnig depending on the exact feeling they want to express.