Μην ανησυχείς, η συνάδελφός μου αστειεύεται συχνά όταν είναι κουρασμένη.

Because Greek forms negative commands with μη(ν) + the verb, rather than with a special negative imperative form.

So:

• ανησυχείς = you worry / you are worrying
• μην ανησυχείς = don’t worry

In other words, μην is the negative particle used for prohibitions or negative instructions.

Yes. ανησυχείς is 2nd person singular, so it is used when speaking to one person informally.

If you wanted to say it politely to one person, or to more than one person, you would usually say:

• Μην ανησυχείτε = don’t worry

So the sentence as written is addressing one person casually.

Greek normally keeps the definite article with possessive expressions.

So Greek says:

• η συνάδελφός μου
  literally: the colleague my

but naturally: my colleague

This is very normal in Greek:

• ο φίλος μου = my friend
• η αδερφή μου = my sister
• το σπίτι μου = my house

So the article is not extra emphasis here; it is just standard Greek grammar.

The basic noun is η συνάδελφος.

When certain words are followed by an enclitic such as μου, σου, του, της, Greek often adds a second written accent to keep the stress pattern clear.

So:

• η συνάδελφος
• η συνάδελφός μου

This does not mean the word has changed meaning or case. It is the same noun; the extra accent appears because μου follows it.

It can be either, depending on context.

συνάδελφος is one of those Greek nouns whose form can refer to a man or a woman. The gender becomes clear from things like:

• the article: ο or η
• adjectives or participles that agree with it

Here we have:

• η συνάδελφός μου → female
• κουρασμένη → feminine form

So in this sentence, the colleague is definitely female.

Because Greek weak possessive pronouns usually come after the noun.

So Greek says:

• η συνάδελφός μου = my colleague
• το βιβλίο μου = my book

English puts the possessive before the noun, but Greek usually places μου, σου, του, της after it.

It is the 3rd person singular present of αστειεύομαι, which means to joke or to kid around.

So:

• αστειεύομαι = I joke
• αστειεύεται = he/she jokes, he/she is joking

A useful thing to notice is that this verb has middle/passive-style endings but an active meaning. So even though it looks like a passive form to an English speaker, here it simply means she is joking or she jokes.

Because Greek often leaves out subject pronouns when the meaning is already clear.

In the clause:

• όταν είναι κουρασμένη

Greek does not need to say αυτή είναι κουρασμένη, because the person is already understood from the previous clause: η συνάδελφός μου.

This is very common in Greek. The verb form and the context usually make the subject clear enough.

Because it must agree with η συνάδελφός μου, which is feminine singular.

The adjective κουρασμένος means tired, and it changes for gender:

• κουρασμένος = masculine
• κουρασμένη = feminine
• κουρασμένο = neuter

Since the colleague is female, Greek uses:

• κουρασμένη

Not necessarily. In this sentence, the present tense expresses a habitual or general action.

So:

• αστειεύεται συχνά = she often jokes
• όταν είναι κουρασμένη = when she is tired

This means something like she tends to joke when she’s tired, not only that it is happening at this exact moment.

Greek, like English, often uses the present tense for habits and repeated behavior.

συχνά means often. It is an adverb modifying αστειεύεται.

So:

• αστειεύεται συχνά = she jokes often

Greek word order is fairly flexible, so you may also hear things like:

• συχνά αστειεύεται
• αστειεύεται όταν είναι κουρασμένη συχνά — less natural in this sentence

The version in your sentence is very natural and neutral. It places often right after the verb phrase, before the when clause.