Me di un golpe en la cabeza al bajar del coche.

Because darse un golpe is a very common Spanish expression meaning to hit oneself / to bang oneself / to get a knock.

So me di un golpe literally breaks down as:

• me = myself / to myself
• di = I gave
• un golpe = a blow / a hit

Literally: I gave myself a hit
Natural English: I banged my head / I hit myself / I got a knock

In Spanish, this kind of idea is often expressed with a reflexive pronoun, even where English would not use one.

Me di un golpe is a very natural, everyday way to say that you accidentally knocked or banged yourself.

It often suggests a single impact, for example:

• Me di un golpe en la rodilla.
• Me di un golpe en la cabeza.

You could also say me golpeé, but that can sound a bit more direct or less idiomatic in everyday speech depending on context. In many situations, darse un golpe is the more common colloquial choice for accidental bumps and knocks.

So:

• me di un golpe = I bumped/knocked myself; I got hit
• me golpeé = I hit myself

Both can work, but me di un golpe is very common and natural.

Spanish often uses a noun where English prefers a verb-only structure.

So instead of saying:

• I hit my head

Spanish very naturally says:

• Me di un golpe en la cabeza
  • literally: I gave myself a blow on the head

This sounds completely normal in Spanish. It is just a different way of packaging the event.

Other similar examples:

• Me di un golpe en el brazo = I banged my arm
• Se dio un golpe en la pierna = He/She banged his/her leg

Because darse un golpe en is the normal pattern in Spanish when talking about the part of the body where the impact happened.

So:

• Me di un golpe en la cabeza
• Se dio un golpe en la espalda
• Nos dimos un golpe en la rodilla

Here en means something like on or in the area of.

Using a la cabeza would not sound right in this structure.

Spanish very often uses the definite article (el, la, los, las) with body parts when the owner is already clear from the reflexive pronoun or context.

So:

• Me duele la cabeza = My head hurts
• Me lavé las manos = I washed my hands
• Me di un golpe en la cabeza = I hit my head

The me already tells you whose head it is, so Spanish normally says la cabeza, not mi cabeza.

Saying mi cabeza is possible in some contexts, but here it would sound less natural.

Di is the preterite form of dar for yo.

• infinitive: dar = to give
• preterite, yo: di = I gave

In this sentence, the preterite is used because it describes a completed event: one specific moment when the speaker banged their head.

A quick mini-conjugation of dar in the preterite:

• yo di
• tú diste
• él/ella dio
• nosotros dimos
• vosotros disteis
• ellos/ellas dieron

So me di un golpe = I banged myself / I got a knock.

Al + infinitive is a very common Spanish structure meaning:

• when ...
• upon ...
• while ...
• as ...

depending on context.

So:

• al bajar del coche = when getting out of the car / as I was getting out of the car

It comes from:

• a + el = al
• bajar = to get down / to go down / to get out

Other examples:

• Al entrar, saludó a todos. = When he came in, he greeted everyone.
• Al abrir la puerta, vio a su amigo. = On opening the door, she saw her friend.

In your sentence, al bajar del coche gives the time/context in which the accident happened.

Yes. In Spain, bajar del coche is a normal way to say to get out of the car, especially with the sense of physically getting down/out from it.

Literally:

• bajar = to go down / get down
• del coche = from the car

So literally it is something like to get down from the car, but in context it means to get out of the car.

You may also hear:

• salir del coche = to get out of the car

Both are possible, but bajar del coche is very idiomatic.

Because de + el contracts to del.

So:

• de + el coche → del coche

This contraction is required in normal Spanish.

The only common exception is when el is part of a proper name, for example:

• de El Escorial

But here el is just the article, so it must become del.

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

So for Spanish from Spain, this sentence sounds completely natural:

• al bajar del coche

In many parts of Latin America, people might say:

• carro
• auto

But since this is Spain Spanish, coche is the expected choice.

Yes, that is possible, and it would mean roughly the same thing.

Compare:

• Me di un golpe en la cabeza = I banged my head / I got a knock on the head
• Me golpeé la cabeza = I hit my head

The first one is especially idiomatic for accidental knocks or bumps. The second is also correct, but the nuance can feel slightly different.

Very often, native speakers prefer darse un golpe for this kind of accidental everyday mishap.

Yes. Spanish often leaves the subject unstated because the verb form and context make it clear.

In this sentence:

• Me di already tells us the subject is I
• so al bajar del coche is understood as when I was getting out of the car

Spanish does not need to repeat yo unless there is a reason to emphasize it.

So the sentence naturally means:

• I banged my head when getting out of the car

not someone else getting out of the car.

A close literal breakdown would be:

• Me = myself / to myself
• di = I gave
• un golpe = a blow / a hit
• en la cabeza = on the head
• al bajar = on/upon getting out
• del coche = from the car

So very literally:

I gave myself a hit on the head upon getting out of the car.

That is not natural English, but it helps show how the Spanish sentence is built. The natural English meaning is something like:

I banged my head getting out of the car.