Коли повертається апетит, я розумію, що справді одужую.

Because апетит is the subject of the verb повертається.

In Коли повертається апетит..., the thing doing the action is appetite: it returns. So Ukrainian uses the nominative:

• апетит = nominative singular
• повертається апетит = appetite returns

Even though in English we might think of getting one’s appetite back, Ukrainian structures this more directly as appetite returns.

The -ся makes the verb reflexive or, more broadly, marks a verb that is used in an intransitive/reflexive way.

Here, повертатися means to return / to come back. So:

• повертати = to return something / to turn something back
• повертатися = to return, to come back

In this sentence, no one is actively returning the appetite; rather, the appetite comes back on its own:

• Коли повертається апетит = When my appetite comes back

This is very natural Ukrainian.

Both are possible.

• Коли повертається апетит
• Коли апетит повертається

The version in your sentence puts the verb first in the subordinate clause, which is very natural in Ukrainian and can sound a bit smoother or more dynamic in context.

A rough way to think about it:

• Коли повертається апетит → slight focus on the event of returning
• Коли апетит повертається → slightly more neutral or straightforward

This is mostly a matter of word order and emphasis, not a big change in meaning.

Here коли can be understood as when, and in some contexts it can also feel like whenever.

In this sentence, it introduces a time clause:

• Коли повертається апетит, я розумію...
• When my appetite returns, I realize...

Because the sentence expresses a general sign of recovery, English could also paraphrase it as:

• Whenever my appetite comes back, I realize...

But when is the most direct translation.

Because the sentence describes what happens at that moment or as a general pattern.

1. повертається

returns / is returning

2. я розумію

I realize / I understand

3. одужую

I am recovering / getting better

Ukrainian often uses the present tense in statements like this even if English might sometimes prefer a slightly different feel. The idea is:

• when appetite comes back,
• at that point I realize
• that I really am recovering.

So the present tense is completely natural.

This is a very useful aspect question.

• одужую = imperfective, I am recovering / getting better
• одужаю = perfective future, I will recover / I’ll get well

In your sentence, the speaker means they are in the process of getting better, not that the recovery is completely finished. So одужую fits better:

• що справді одужую = that I’m really recovering / getting better

If you said що справді одужаю, that would sound more like:

• that I really will recover

That is a different meaning.

Що introduces a subordinate clause, like that in English.

• я розумію, що справді одужую
• I realize that I am really recovering

So the structure is:

• main clause: я розумію
• subordinate clause: що справді одужую

In everyday English, that is often omitted: I realize I’m really recovering. In Ukrainian, що is normally expressed here.

Yes, here справді means really, truly, or indeed.

So:

• що справді одужую = that I really am recovering

It adds emphasis: the speaker is not just hoping they are getting better; they recognize it as genuinely true.

A few near-equivalents are:

• справді
• дійсно

Both can often mean really / truly / indeed.

One thing to watch out for: насправді often means actually / in fact, which is similar but not always identical in tone.

Because Коли повертається апетит is a subordinate clause placed before the main clause.

Ukrainian punctuation separates subordinate clauses with commas:

• Коли повертається апетит, я розумію...

This is similar to English:

• When my appetite returns, I realize...

So the comma is required.

Yes, often it can.

Ukrainian frequently drops subject pronouns when the verb ending already makes the subject clear.

So these are both possible:

• Коли повертається апетит, я розумію, що справді одужую.
• Коли повертається апетит, розумію, що справді одужую.

The version with я is a bit more explicit and can sound slightly more personal or emphatic. The version without it is also natural if the subject is obvious from context.

Yes, this is a very normal way to express the idea.

Common Ukrainian phrasing includes:

• апетит повертається = appetite returns
• до мене повертається апетит = my appetite is coming back / appetite is returning to me

So instead of literally saying I get my appetite back, Ukrainian often makes апетит the subject:

• Апетит повертається.
• У мене повернувся апетит. = My appetite came back.

All of these are natural, depending on context.

Grammatically, yes: розумію literally means I understand. But in this context, I realize is usually more natural English.

Compare:

• я розумію, що... = literally I understand that...
• in context: I realize that...

Why? Because the speaker is recognizing a sign of improvement. In English, realize often fits this moment of recognition better than understand.

So both are possible, but I realize is the more idiomatic translation here.

Yes. Ukrainian word order is flexible.

For example:

• Я розумію, що справді одужую, коли повертається апетит.

This still makes sense and means essentially the same thing. But the original version is usually more natural because it starts with the when-clause and sets up the situation first:

• Коли повертається апетит, я розумію...

That order feels very natural for: When X happens, I realize Y.

So the original sentence is a good, idiomatic choice.