Με ξαφνιάζει το ότι μιλάς τόσο ήρεμα όταν έχεις τόσο άγχος.

Με is the weak form of the pronoun εμένα / me, and here it means me as the object of the verb.

So:

• Με ξαφνιάζει = It surprises me

Greek often puts these short object pronouns before the verb.

Because the subject of the sentence is not I. The thing doing the surprising is the whole clause:

το ότι μιλάς τόσο ήρεμα όταν έχεις τόσο άγχος

That whole part functions as a singular idea, so the verb is in 3rd person singular:

• ξαφνιάζω = I surprise
• ξαφνιάζεις = you surprise
• ξαφνιάζει = it surprises

So literally the structure is:

• [The fact that you speak so calmly when you have so much anxiety] surprises me

Το ότι means something like the fact that.

It turns the following clause into a noun-like unit:

• το ότι μιλάς τόσο ήρεμα... = the fact that you speak so calmly...

This is very common in Greek when a whole statement is treated as the subject or object of another verb.

Without going too deep:

• ότι by itself = that
• το ότι = the fact that

So το is not translating as a normal the word-for-word; it helps package the clause as a thing.

Yes, in some contexts Greek can use other structures, especially που in everyday speech:

• Με ξαφνιάζει που μιλάς τόσο ήρεμα...

This is very natural and common.

Το ότι often sounds a bit more explicit or slightly more formal, because it really highlights the fact that.

So:

• Με ξαφνιάζει το ότι... = a bit more structured/formal
• Με ξαφνιάζει που... = very common, everyday Greek

Μιλάς is the 2nd person singular present of μιλάω / μιλώ:

• μιλάω = I speak
• μιλάς = you speak

It matches the implied you in the sentence.

Greek usually does not need an explicit subject pronoun like εσύ, because the verb ending already shows who the subject is.

So μιλάς already means you speak / you are speaking.

Because ήρεμα is an adverb, while ήρεμος is an adjective.

Here the sentence describes how someone speaks, so Greek uses the adverb:

• ήρεμος = calm (describing a person, masculine adjective)
• ήρεμα = calmly (describing the manner of speaking)

So:

• μιλάς ήρεμα = you speak calmly

This is very common in Greek: many adverbs look like the neuter singular form of the adjective.

Τόσο means so, so much, or to such a degree.

In this sentence it appears twice:

• τόσο ήρεμα = so calmly
• τόσο άγχος = so much anxiety / such anxiety

It emphasizes degree.

This repetition is very natural in Greek and creates a contrast:

• you speak so calmly
• even though you have so much anxiety

Both are possible, but they are not exactly the same in tone.

• πολύ άγχος = a lot of anxiety
• τόσο άγχος = so much anxiety

Τόσο is stronger and more expressive. It often sets up a contrast or emotional reaction.

Since the sentence is about being surprised, τόσο fits very well:

• You speak so calmly when you have so much anxiety

It sounds more pointed than πολύ.

Όταν means when.

It introduces the time/situation in which the calm speaking happens:

• όταν έχεις τόσο άγχος = when you have so much anxiety

This is not a condition like if; it is a real circumstance, so όταν is the natural choice.

Because the sentence describes a present or general situation:

• μιλάς = you speak / you are speaking
• έχεις = you have

Greek present tense often covers both:

• a current action/state
• a habitual or general one

So this can mean either:

• right now, you are speaking calmly although you are anxious
• more generally, you tend to speak calmly when you are anxious

The exact reading depends on context.

It is the direct object of έχεις, so grammatically it is in the accusative.

However, άγχος is a neuter noun, and for many neuter nouns the nominative and accusative look the same. So you do not see a different ending here.

That is why:

• το άγχος can be nominative
• το άγχος can also be accusative

In this sentence it is accusative because it is the thing you have.

Greek word order is more flexible than English word order.

This sentence begins with:

• Με ξαφνιάζει...

That is a very natural way to say It surprises me...

But Greek could also move things around for emphasis, for example:

• Το ότι μιλάς τόσο ήρεμα όταν έχεις τόσο άγχος με ξαφνιάζει.

This version puts the whole subject first, more like formal written English.

So the original order is natural and smooth, especially in normal speech.

No. This is a very common learner question.

• ότι = that
• ό,τι = whatever / anything that

In your sentence, it is ότι without the extra comma-like separation in writing, because it introduces a content clause:

• το ότι μιλάς... = the fact that you speak...

So this is definitely ότι = that, not ό,τι = whatever.

Usually yes, in this kind of sentence.

Ξαφνιάζω / ξαφνιάζομαι is related to the idea of being taken aback or caught off guard. In many contexts, surprise is the best translation.

Here it suggests that the speaker finds the contrast unexpected:

• calm speaking
• despite a lot of anxiety

So surprises me is a very natural understanding.