Anoche estaba bajando la persiana cuando se rompió.

Because estaba bajando presents the action as in progress/background at that moment: I was in the middle of lowering it. Spanish commonly uses imperfect (often with estar + gerundio) to set the scene, and then uses preterite for the event that happens and changes the situation.

Se rompió is in the preterite because it’s a completed, punctual event: it broke (at a specific moment). In this structure, the preterite often marks the interrupting event that happens while another action is ongoing.

Cuando here is like when = “at the moment that…” and it often introduces the interrupting event:

• Estaba bajando… cuando se rompió = I was lowering it when it broke.

Mientras (“while”) emphasizes two ongoing actions happening at the same time. You could say Mientras bajaba la persiana, se rompió, but cuando is especially common for the “ongoing action + sudden event” pattern.

Se rompió means it broke (intransitive). The se is used with many verbs to show something became broken without stating an agent. It often avoids saying who did it, and it can feel more like “it broke” than “someone broke it.”

If you want to explicitly say someone broke it, you’d use:

• La rompí / Alguien la rompió = I broke it / Someone broke it.

Yes. Se me rompió is very common and adds the idea of an unintentional/accidental event that affected you:

• Anoche estaba bajando la persiana cuando se me rompió ≈ …when it broke on me / …when it broke (accidentally, to my dismay).

It doesn’t literally mean it broke “to me,” but it signals lack of intention and personal impact.

Persiana usually refers to a window blind/shutter, often something you can raise/lower (like slats or a rolling shutter).
In many Latin American regions, people might also say cortina (curtain) or persiana depending on the exact type and local preference.

So the sentence is about lowering a blind/shutter and it broke.

Both are correct:

• estaba bajando la persiana
• estaba bajándola (with la = “it”)

Spanish often keeps the noun (la persiana) for clarity, especially if it’s being introduced or emphasized. Using la is common when it’s already obvious what you’re talking about.

With estar + gerundio, you have two standard options: 1) Before the conjugated verb: la estaba bajando
2) Attached to the gerund: estaba bajándola (note the written accent to keep the stress)

Both mean the same thing.

Bajando doesn’t need an accent because it naturally follows Spanish stress rules.
When you attach pronouns (-la, -lo, -me, etc.) to a gerund, Spanish often adds an accent to preserve the original stress:

• bajando → bajándola

Yes. Anoche (“last night”) can appear with imperfect when you’re describing a background situation happening at a certain time last night:

• Anoche estaba bajando… = Last night I was (in the middle of) lowering…

If you were narrating a completed action, you’d more likely use preterite:

• Anoche bajé la persiana = Last night I lowered the blind (completed action).

You can say Anoche estuve bajando la persiana, but it changes the feel:

• Estuve bajando (preterite) often suggests a bounded period/attempt: “I spent some time lowering it / I was lowering it (for a while).”
• Estaba bajando focuses on the ongoing moment when something happened.

With cuando se rompió, estaba bajando is the most natural choice for the classic “was doing X when Y happened” narrative.