Nos pasamos la mañana empujando cajas por el pasillo y arrastrando maletas durante la mudanza.

Because Spanish very often uses pasarse to express spending a period of time doing something, especially when the idea is we ended up spending that whole time on it.

So:

Nos pasamos la mañana empujando cajas...
= We spent the morning pushing boxes...

The nos is the reflexive pronoun for we.

You can also hear pasamos la mañana..., but nos pasamos la mañana... often sounds a bit more emphatic, as if that activity took up the whole morning.

The pattern is:

pasarse + a period of time + gerund

Examples:

• Me pasé la tarde estudiando. = I spent the afternoon studying.
• Se pasaron el verano viajando. = They spent the summer travelling.
• Nos pasamos la mañana empujando cajas. = We spent the morning pushing boxes.

This is a very common way to talk about how time was occupied.

Because here la mañana is not just saying in the morning. It is the time period that was spent.

Compare:

• Por la mañana empujamos cajas. = In the morning we pushed boxes.
• Nos pasamos la mañana empujando cajas. = We spent the morning pushing boxes.

So la mañana works as the time expression after pasarse.

Because after pasarse + time period, Spanish normally uses a gerund to say what someone spent that time doing.

So:

• Nos pasamos la mañana empujando cajas...
• Se pasó el día trabajando.

In this structure, the gerund is the natural choice. English often uses spent the morning doing..., and Spanish matches that idea with gerundio.

Spanish does have y there: empujando cajas por el pasillo y arrastrando maletas...

What is happening is that both gerunds depend on the same earlier structure:

Nos pasamos la mañana [empujando cajas...] y [arrastrando maletas...]

Spanish does not need to repeat nos pasamos la mañana before the second action. English works the same way:

We spent the morning pushing boxes and dragging suitcases...

Here por means something like along, down, or through the corridor/hallway, depending on context.

So:

• empujando cajas por el pasillo

suggests moving the boxes along the corridor.

This is a very common use of por for movement through or along a place:

• caminar por la calle = walk along the street
• correr por el parque = run through the park

It is not for the corridor here.

Because Spanish often leaves out the article when talking about plural countable things in a general, indefinite way.

So:

• empujando cajas
• arrastrando maletas

means pushing boxes and dragging suitcases, not specific previously identified ones.

If you said las cajas or las maletas, it would sound more like the boxes or the suitcases, meaning particular ones already known in the conversation.

Durante means during, so it focuses on the activity happening throughout that event or within that period.

• durante la mudanza = during the move / during the house move

You might sometimes hear en la mudanza, but durante is clearer here because the sentence is about actions taking place while the move was happening.

In Spain, mudanza commonly means a house move / moving home / the process of moving belongings from one place to another.

So durante la mudanza means during the move.

It refers to the event or process, not just the furniture or the removal company.

Yes. That would also be correct and natural.

Difference in feel:

• Pasamos la mañana empujando cajas... = We spent the morning pushing boxes...
• Nos pasamos la mañana empujando cajas... = We spent the whole morning pushing boxes... / We ended up spending the morning...

The version with nos pasamos often sounds a bit more vivid or slightly more colloquial, with more emphasis on how the time was taken up.

Yes. Spanish allows some flexibility.

For example:

• Durante la mudanza, nos pasamos la mañana empujando cajas por el pasillo y arrastrando maletas.
• Nos pasamos la mañana, durante la mudanza, empujando cajas por el pasillo y arrastrando maletas.

The original position, at the end, is very natural. It works as extra context for the whole sentence.

Even if the general meaning is already clear, the nuance is useful:

• empujar = to push
  You apply force and move something away from you or ahead of you.
• arrastrar = to drag
  You pull or haul something, often with contact against the ground.

So the sentence paints a physical scene very clearly:

• boxes being pushed down the corridor
• suitcases being dragged during the move

Yes, it sounds natural in Spain.

In particular:

• nos pasamos la mañana + gerund
• por el pasillo
• durante la mudanza

all sound normal and idiomatic.

A native speaker in Spain would easily understand it as a natural description of a tiring morning spent moving things around.