Ζαλίζομαι όταν σηκώνομαι πολύ γρήγορα από την καρέκλα.

Not necessarily. In Greek, a verb ending in -ομαι is in the mediopassive form, but that does not always mean it is truly passive in meaning.

In this sentence:

• ζαλίζομαι = I get dizzy / I feel dizzy
• σηκώνομαι = I get up / I stand up

These are both very common verbs that often appear in this form with an active meaning in English.

So here:

• ζαλίζω = I make someone dizzy
• ζαλίζομαι = I get dizzy / I feel dizzy

and

• σηκώνω = I lift, raise
• σηκώνομαι = I get up, stand up

So the -ομαι ending is important, but you should not automatically translate it as English passive.

Greek often drops the subject pronoun because the verb ending already shows who the subject is.

For example:

• ζαλίζομαι already means I get dizzy
• σηκώνομαι already means I get up

So εγώ is usually unnecessary unless you want emphasis or contrast.

For example:

• Εγώ ζαλίζομαι, αλλά αυτός όχι.
  I get dizzy, but he doesn’t.

In your sentence, no emphasis is needed, so leaving out εγώ is the most natural choice.

Here ζαλίζομαι means I get dizzy or I feel dizzy.

It can refer to:

• physical dizziness
• feeling faint
• sometimes even mental confusion, depending on context

In this sentence, because it happens when the person stands up quickly, it clearly refers to physical dizziness.

A useful contrast is:

• ζαλίζω κάποιον = I make someone dizzy
• ζαλίζομαι = I get dizzy

So the sentence is describing something that happens to the speaker.

This is a very common and useful pair.

• σηκώνω = I lift / I raise something
• σηκώνομαι = I get up / I stand up

Examples:

• Σηκώνω το κουτί. = I lift the box.
• Σηκώνομαι από την καρέκλα. = I get up from the chair.

So in your sentence, σηκώνομαι is the correct form because the speaker is not lifting something else; the speaker is getting up.

Because the sentence describes a general, repeated situation:

• I get dizzy when I stand up very quickly from the chair.

In Greek, when όταν means when/whenever in a habitual or repeated sense, it often takes the present tense.

So:

• ζαλίζομαι = I get dizzy
• όταν σηκώνομαι = when I get up / whenever I get up

This is similar to English sentences like:

• I feel tired when I work late.
• I sneeze when I’m near cats.

If you were talking about one specific past event, you would normally use past forms instead:

• Ζαλίστηκα όταν σηκώθηκα πολύ γρήγορα από την καρέκλα.
  I got dizzy when I stood up very quickly from the chair.

In this sentence, it is closer to whenever in meaning, even though English often just says when.

The idea is not one single event, but a repeated pattern:

• every time / whenever I stand up very quickly, I get dizzy

So όταν can introduce:

• a specific when
• a repeated whenever

The exact interpretation comes from context.

Because γρήγορα is an adverb meaning quickly, and πολύ means very.

So:

• γρήγορα = quickly
• πολύ γρήγορα = very quickly

This is just like English very quickly, where one word modifies the adverb.

Note that πολύ can modify different kinds of words:

• πολύ καλός = very good
• πολύ γρήγορα = very quickly
• πολύ νερό = a lot of water

So here it intensifies the manner of getting up.

Because από means from.

So:

• από την καρέκλα = from the chair

With verbs like σηκώνομαι, Greek commonly uses από to show the place you are rising from:

• σηκώνομαι από το κρεβάτι = I get up from the bed
• σηκώνομαι από τον καναπέ = I get up from the sofa
• σηκώνομαι από την καρέκλα = I get up from the chair

Also notice that από is followed by the accusative:

• την καρέκλα

Greek uses the definite article very often, more often than English does.

Here την καρέκλα literally means the chair. In context, this sounds natural because it refers to the chair the speaker is sitting on.

Greek often prefers the article in everyday situations where English may or may not use it. So even if English says from a chair or simply from the chair depending on context, Greek commonly uses:

• από την καρέκλα

It feels specific and natural in the situation being described.

It is in the accusative singular.

That is because από takes the accusative in Modern Greek.

So:

• η καρέκλα = the chair (nominative)
• την καρέκλα = the chair (accusative)

You can see the article change:

• nominative: η
• accusative: την

This is a very common pattern with feminine nouns.

They are both in the present tense.

But here the present tense does not mean only right now. It expresses a habitual or general action:

• Ζαλίζομαι = I get dizzy / I tend to get dizzy
• όταν σηκώνομαι = when(ever) I get up

Greek present tense often works this way, just like English present in sentences such as:

• I get headaches when I don’t sleep enough.
• I feel cold when I sit still too long.

So this sentence describes a regular reaction, not necessarily something happening at this exact moment.

Yes. Greek word order is more flexible than English, although some orders sound more natural than others.

The original sentence is very natural:

• Ζαλίζομαι όταν σηκώνομαι πολύ γρήγορα από την καρέκλα.

You could also say:

• Όταν σηκώνομαι πολύ γρήγορα από την καρέκλα, ζαλίζομαι.

This puts more focus on the when-clause first, a bit like English:

• When I stand up very quickly from the chair, I get dizzy.

Both are correct. The original version is slightly more conversational and direct.

Not exactly.

• ζαλίζομαι focuses on the experience or process: I get dizzy / I feel dizzy
• είμαι ζαλισμένος or είμαι ζαλισμένη focuses more on the state: I am dizzy

So:

• Ζαλίζομαι όταν σηκώνομαι πολύ γρήγορα.
  I get dizzy when I stand up very quickly.

• Είμαι ζαλισμένος / ζαλισμένη τώρα.
  I am dizzy now.

In many situations they are similar, but the first often sounds more like this happens to me, while the second sounds more like this is my current condition.

Because it describes how the action happens.

In the sentence:

• σηκώνομαι πολύ γρήγορα

the word γρήγορα describes the verb σηκώνομαι. It tells us how the person gets up: quickly.

That makes it an adverb.

Compare:

• γρήγορος = quick, fast (adjective, masculine)
• γρήγορη = quick, fast (adjective, feminine)
• γρήγορο = quick, fast (adjective, neuter)
• γρήγορα = quickly (adverb)

So here we need the adverb, because we are describing the action, not a noun.

Yes, in many everyday contexts you could.

For example:

• Ζαλίζομαι άμα σηκώνομαι πολύ γρήγορα από την καρέκλα.

This is more informal and conversational.

Very roughly:

• όταν = when
• άμα = when / if, often in spoken Greek

In a neutral, standard sentence, όταν is the safest and most common choice.

Then Greek would normally use past forms instead of the present.

You would say:

• Ζαλίστηκα όταν σηκώθηκα πολύ γρήγορα από την καρέκλα.

That means:

• I got dizzy when I stood up very quickly from the chair.

Compare the two patterns:

• Ζαλίζομαι όταν σηκώνομαι... = repeated / general situation
• Ζαλίστηκα όταν σηκώθηκα... = one completed past event

This is a very useful contrast in Greek.