Έχοντας κοιμηθεί μόνο τέσσερις ώρες, δεν ήμουν καθόλου συγκεντρωμένος στο μάθημα.

It is an adverbial participial phrase meaning having slept.

More specifically:

• έχοντας = the adverbial participle of έχω (having)
• κοιμηθεί = the non-finite perfective form of κοιμάμαι (slept)

Together, έχοντας κοιμηθεί expresses an action that was completed before the action in the main clause.

So the structure is:

• Έχοντας κοιμηθεί μόνο τέσσερις ώρες, ...
• Having slept only four hours, ...

This is a fairly common way in Greek to express after doing X or because one had done X.

Because the sentence needs the idea of completed action before the main event.

• Έχοντας κοιμηθεί = having slept
• κοιμώντας = sleeping / while sleeping

These are not the same.

In this sentence, the speaker means:

• first: they slept only four hours
• then: they were not focused in class

So Greek uses έχοντας + κοιμηθεί to show that the sleeping happened earlier and was already finished.

If you said κοιμώντας μόνο τέσσερις ώρες, it would sound more like while sleeping only four hours or by sleeping only four hours, which is not the intended meaning here.

κοιμηθεί is the perfective non-finite form of κοιμάμαι.

English speakers often notice that it looks like neither a normal finite verb form nor a participle like an adjective. That is because in Modern Greek, forms like κοιμηθεί are used in structures such as:

• έχω κοιμηθεί = I have slept
• να κοιμηθεί = for him/her to sleep / that he/she sleep
• έχοντας κοιμηθεί = having slept

You do not need to think of it as a standalone tense. It is a form used together with other elements like έχω, να, or έχοντας.

ήμουν is the imperfect of είμαι (I was).

It is used because the speaker is describing a state in the past:

• δεν ήμουν καθόλου συγκεντρωμένος = I was not at all focused

The imperfect is very natural here because it presents the lack of concentration as an ongoing or background state during the class.

Aorist would not work with είμαι in the same way in standard Modern Greek for this meaning. Greek normally uses the imperfect of είμαι to say was.

Because δεν is the standard negation used with indicative verbs in Modern Greek.

Here the main clause is:

• δεν ήμουν καθόλου συγκεντρωμένος στο μάθημα

So:

• ήμουν = I was
• δεν ήμουν = I was not

A useful point: δεν negates the main verb, while μη(ν) is generally used in other environments such as the subjunctive, imperatives, and certain fixed expressions.

καθόλου means at all in this sentence.

So:

• δεν ήμουν συγκεντρωμένος = I wasn’t focused
• δεν ήμουν καθόλου συγκεντρωμένος = I wasn’t focused at all

It strengthens the negation.

Be careful: καθόλου can sometimes mean something like not at all with negatives, but in other contexts it may have slightly different uses depending on tone and context. Here it clearly intensifies δεν ήμουν.

Because συγκεντρωμένος is an adjective (or adjectival participle) agreeing with the speaker.

It must match the person being described in:

• gender
• number
• case

Here it is:

• masculine singular nominative: συγκεντρωμένος

So this sentence suggests that the speaker is male.

If the speaker were female, it would be:

• δεν ήμουν καθόλου συγκεντρωμένη στο μάθημα

This is very common in Greek: past states are often expressed with είμαι + adjective.

Because τέσσερις ώρες is the normal way to express duration: four hours.

• τέσσερις = four (feminine/plural form, agreeing with ώρες)
• ώρες = hours

Since ώρα is feminine, the numeral appears in the matching form:

• τέσσερις ώρες

Greek often uses the accusative to express how long something lasts. So this is essentially for four hours, even though Greek does not need a separate word for for here.

Because μόνο modifies the amount of sleep: only four hours.

So:

• κοιμηθεί μόνο τέσσερις ώρες = slept only four hours

Its position is natural because it directly highlights the limited quantity.

Greek word order is somewhat flexible, but this placement is the most straightforward. Putting μόνο elsewhere could change what is being emphasized.

For example:

• μόνο τέσσερις ώρες = emphasis on the small number of hours
• κοιμηθεί μόνο would sound incomplete unless more followed

στο μάθημα literally means in the lesson/class.

It is:

• σε
  • το = στο
• μάθημα = lesson / class / course session

In this sentence, it most naturally means in class or during class.

So στο μάθημα tells you the context in which the speaker was not focused.

Usually both.

It can be understood as:

• after sleeping only four hours (time)
• because I had slept only four hours (cause)

Greek often allows this kind of overlap in participial phrases. In real context, listeners naturally understand that the lack of sleep is the reason for the lack of concentration, while also being something that happened before the class.

So the phrase is not just chronological; it strongly suggests a causal connection too.

Yes, normally it does.

In this sentence, the understood subject of Έχοντας κοιμηθεί is the same person as the subject of ήμουν:

• I, having slept only four hours, was not at all focused in class.

This is the normal rule with adverbial participial phrases in Greek: the understood subject is usually the same as the subject of the main clause.

If the subjects were different, the sentence would usually need a different structure to avoid confusion.

Yes. A more explicit version could be:

• Επειδή είχα κοιμηθεί μόνο τέσσερις ώρες, δεν ήμουν καθόλου συγκεντρωμένος στο μάθημα.
• Αφού είχα κοιμηθεί μόνο τέσσερις ώρες, δεν ήμουν καθόλου συγκεντρωμένος στο μάθημα.

These mean roughly:

• Because I had slept only four hours, I wasn’t at all focused in class.

Compared with those, Έχοντας κοιμηθεί... is a bit more compact and slightly more formal or written in feel, though still perfectly natural.

Yes, it is natural and correct.

It sounds like good standard Greek, especially in writing or in more careful speech. The opening participial phrase Έχοντας κοιμηθεί μόνο τέσσερις ώρες is elegant and concise.

In casual speech, many speakers might prefer a clause with επειδή or αφού, but the original sentence is absolutely normal and idiomatic.