Cuando me mareo en el coche, abro la ventana y respiro hondo.

Because cuando here means when as a conjunction: When I feel carsick / when I get dizzy in the car...

With no accent, cuando introduces a clause.

Cuándo with an accent is used in direct or indirect questions:

• ¿Cuándo llegas? = When are you arriving?
• No sé cuándo llega. = I don’t know when he/she is arriving.

So in this sentence, cuando is correct because it is not a question.

Because the verb is marearse, which is commonly used to mean to get dizzy, to feel sick, or to get travel sick / carsick.

So:

• me mareo = I get dizzy / I feel sick
• te mareas = you get dizzy
• se marea = he/she gets dizzy

That me is the reflexive pronoun that goes with marearse.

A learner might first think mareo means I dizzy, but really it is:

• me = myself
• mareo = I make dizzy / I get dizzy as part of the reflexive verb marearse

In everyday Spanish, marearse is very natural for motion sickness.

It can mean either, depending on context.

In Cuando me mareo en el coche..., the context en el coche strongly suggests motion sickness, so a natural English interpretation is:

• When I get carsick in the car... or
• When I feel sick/dizzy in the car...

Spanish often uses marearse in situations where English might use:

• to feel dizzy
• to feel nauseous
• to get carsick
• to get motion sick

The exact English translation depends on context.

Because en el coche means in the car, referring to being inside a specific type of place/vehicle.

• en el coche = in the car
• en coche = by car / by means of a car

Compare:

• Me mareo en el coche. = I feel sick in the car.
• Voy al trabajo en coche. = I go to work by car.

So here the sentence is about location/situation, not means of transport.

Spanish often uses the definite article (el, la, los, las) where English would use a possessive like my, his, or their, especially when the owner is obvious from the context.

So:

• abro la ventana literally = I open the window
• natural English = I open the window or sometimes I open my window, depending on context

Spanish prefers la ventana because it is already clear whose action it is: I am opening it.

This is very common:

• Me lavo las manos. = I wash my hands.
• Cierro los ojos. = I close my eyes.

Because Spanish often uses the present tense to talk about habitual actions or what usually happens.

So this sentence means something like:

• When I get carsick in the car, I open the window and take a deep breath.

It is not necessarily happening right now. It describes a repeated or typical reaction.

This is very common in both Spanish and English:

• Cuando estoy cansado, me acuesto temprano. = When I’m tired, I go to bed early.

Because in Spanish, when cuando refers to a habitual or general situation, the present tense is used in both parts:

• Cuando me mareo..., abro... y respiro...

Spanish does not use the future here the way English sometimes suggests sequence.

If you are talking about a specific future event, Spanish often uses:

• Cuando me maree, abriré la ventana y respirar é hondo. = When I feel sick, I’ll open the window and take a deep breath.

So:

Habit / general truth

• Cuando me mareo, abro...

Specific future situation

• Cuando me maree, abriré...

Both can relate to dizziness, but they are used a little differently.

• me mareo focuses on the experience or onset: I get dizzy / I feel sick
• estoy mareado describes the state: I am dizzy

In many real situations, both are possible, but the nuance changes slightly.

Examples:

• Cuando me mareo en el coche, abro la ventana.
  When I start feeling sick in the car, I open the window.
• Estoy mareado.
  I’m dizzy.

For motion sickness, marearse is especially common.

Because Spanish usually leaves out subject pronouns when the verb ending already shows who the subject is.

• mareo = I get dizzy
• abro = I open
• respiro = I breathe

The -o ending already tells you the subject is yo.

Including yo is possible, but it is normally only used for emphasis, contrast, or clarity:

• Yo abro la ventana, no tú. = I open the window, not you.

So in a neutral sentence, leaving out yo is the most natural choice.

Respirar hondo is a very common Spanish expression meaning:

• to breathe deeply
• to take a deep breath

So:

• respiro hondo = I breathe deeply / I take a deep breath

Hondo literally means deep, and here it works adverbially in a fixed, natural expression.

You could say respiro profundamente, and it is grammatically correct, but it sounds more formal or less idiomatic in this everyday context.

For natural spoken Spanish, respirar hondo is the phrase learners should remember.

Yes, mostly.

In Spain, coche is the normal everyday word for car.

In many Latin American countries, people are more likely to say:

• carro
• auto
• automóvil

So a Spain-Spanish version naturally says:

• en el coche

A Latin American version might say:

• en el carro or
• en el auto

All are understandable, but coche is especially associated with Spain.

Not with exactly the same meaning.

• cuando me mareo... = when I get sick...
  This suggests something that happens and what you do in that situation.
• si me mareo... = if I get sick...
  This sounds more conditional or possible, not necessarily something that regularly happens.

Compare:

• Cuando me mareo en el coche, abro la ventana.
  When I get carsick in the car, I open the window.
  → this sounds habitual
• Si me mareo en el coche, abriré la ventana.
  If I get carsick in the car, I’ll open the window.
  → this sounds like a possible future situation

So cuando is the better choice for a usual reaction.

A helpful approximation for a native English speaker is:

• mareo ≈ mah-REH-oh
• hondo ≈ ON-doh

A few points:

• In Spanish, h is silent, so hondo begins with the vowel sound.
• mareo has three vowel sounds: ma-re-o
• The stress in mareo falls on re
• The stress in hondo falls on hon

If you want to sound more natural, keep the vowels short and clear:

• a as in father
• e as in bet (but cleaner)
• o as a pure oh sound

Not literally from the Spanish given.

Abro la ventana simply means I open the window.

In English, roll down the window is a very natural way to talk about a car window, especially with older-style windows. But Spanish does not say that here. It just uses the general verb abrir.

If the meaning is specifically about lowering the car window, Spanish could also say:

• bajo la ventanilla

But in this sentence, abro la ventana is perfectly normal and broad in meaning.