Αυτό είναι φυσιολογικό, μην ανησυχείς.

Αυτό literally means this (or this thing), and it is neuter singular.

In this sentence, it points to the situation being talked about, so in natural English it may be translated as either:

• This is normal
• It’s normal

Greek often uses αυτό where English might just say it.

Because it agrees with Αυτό, which is neuter singular.

Greek adjectives change form to match the gender and number of the noun or pronoun they describe. Here:

• αυτό = neuter singular
• φυσιολογικό = neuter singular form of φυσιολογικός (normal)

So:

• Αυτό είναι φυσιολογικό = This is normal

If the subject were feminine or masculine, the adjective would change:

• Αυτή είναι φυσιολογική
• Αυτός είναι φυσιολογικός

είναι means is / are, depending on context. It is the present-tense form of είμαι (to be).

In this sentence:

• Αυτό είναι φυσιολογικό = This is normal

Greek does not need a separate word for it is in the same way English does; είναι already gives the verb is.

Because μην is the negative particle used for commands, wishes, and subjunctive-type constructions, while δεν is used to negate ordinary statements.

So:

• Δεν ανησυχείς = You are not worrying / You don’t worry
• Μην ανησυχείς = Don’t worry

That is a very important Greek pattern:

• δεν = negates facts/statements
• μη(ν) = negates commands or subjunctive forms

ανησυχείς is the 2nd person singular form of ανησυχώ (to worry).

By itself, it can mean:

• you worry
• you are worrying

But after μην, it becomes a negative command:

• μην ανησυχείς = don’t worry

So even though it looks like a present-tense form, here it functions as part of a prohibition.

Because in Modern Greek, negative commands are normally made with:

• μη(ν) + subjunctive-type verb form

So instead of a separate negative imperative, Greek says:

• Μην ανησυχείς = Don’t worry

This is completely standard.

Compare:

• positive command: Ανησύχησε would mean something like Worry! (not something people usually say!)
• negative command: Μην ανησυχείς = Don’t worry

So the structure is normal Greek grammar, not an exception.

Yes. Μην ανησυχείς is singular informal, used when speaking to one person you address as you in a familiar way.

The polite/plural version is:

• Αυτό είναι φυσιολογικό, μην ανησυχείτε.

So:

• ανησυχείς = informal singular
• ανησυχείτε = plural or polite singular

Yes, absolutely.

• Είναι φυσιολογικό = It’s normal
• Αυτό είναι φυσιολογικό = This is normal

Including Αυτό makes the sentence point more directly to a specific thing or situation. Leaving it out sounds a little more general.

Both are natural.

Yes. Greek word order is more flexible than English, though not completely free.

For example, these are both natural:

• Αυτό είναι φυσιολογικό, μην ανησυχείς.
• Μην ανησυχείς, αυτό είναι φυσιολογικό.

The difference is mainly emphasis:

• starting with Αυτό είναι φυσιολογικό emphasizes reassurance about the situation
• starting with Μην ανησυχείς emphasizes calming the person first

Usually, yes. In most contexts, φυσιολογικό is a very natural translation of normal.

It can also carry a sense of:

• natural
• expected
• not unusual

Depending on context, it may sound slightly more like normal in a natural/medical/logical sense than some other Greek words.

So in this sentence, Αυτό είναι φυσιολογικό means something like:

• That’s normal
• That’s perfectly normal

A rough pronunciation guide is:

• Αυτό → af-TO
• είναι → EE-ne
• φυσιολογικό → fee-see-o-lo-yee-KO
• μην → meen
• ανησυχείς → a-nee-see-HEES

So the whole sentence is roughly:

af-TO EE-ne fee-see-o-lo-yee-KO, meen a-nee-see-HEES

The accent marks show which syllable gets the stress:

• αυτό
• είναι
• φυσιολογικό
• ανησυχείς

Stress is important in Greek, so those written accents matter.