basu de nete ite, basutei wo toorisugite simaimasita.

In this sentence, で marks the place where the action happens.

• バスで寝ていて = while sleeping on the bus
• The action is 寝る (to sleep), so バス is treated as the location of that action.

If the verb were 乗る (to ride / get on), then に would be natural:

• バスに乗る = to ride/get on the bus

So:

• バスで寝る = sleep on the bus
• バスに乗る = ride the bus

寝ていて comes from 寝ている, which means to be sleeping or to be asleep.

Breakdown:

• 寝る = to sleep
• 寝ている = be sleeping / be asleep
• 寝ていて = the て-form of 寝ている, used to connect to the next clause

So バスで寝ていて、 means:

• while I was sleeping on the bus, ...
• or I was asleep on the bus, and then ...

It sets up the background situation for what happened next.

Because the sentence is linking two parts together.

• 寝ていた = was sleeping / was asleep
• 寝ていて、... = was sleeping, and ... / while sleeping, ...

The て-form is often used to connect clauses. Here it gives a smooth connection between:

1. being asleep on the bus
2. passing the bus stop

So 寝ていて is not just stating a fact by itself; it is leading into the result.

That is a very common question. Here, を does not mark a typical direct object in the English sense. With motion verbs, を can mark the place that someone moves through, along, or past.

So:

• 道を歩く = walk along the road
• 橋を渡る = cross the bridge
• バス停を通り過ぎる = pass the bus stop

In other words, バス停を通り過ぎる means to go past the bus stop.

通り過ぎる is a compound verb:

• 通る = to pass through / go along
• 過ぎる = to pass, go beyond

Together, 通り過ぎる means:

• to pass by
• to go past
• to overshoot

So バス停を通り過ぎてしまいました means that the speaker went past the bus stop they intended to get off at.

〜てしまう often adds one of these feelings:

1. completion — something ended completely
2. regret / unfortunate result
3. accidentally / unintentionally

Here, the important nuance is regret / unfortunate result.

So:

• 通り過ぎました = passed the bus stop
• 通り過ぎてしまいました = ended up passing the bus stop / accidentally passed the bus stop / unfortunately missed the stop

It sounds like: Oops, I missed it.

In Japanese, it is natural to say it this way even though in English we might think of the bus as the thing that physically passed the stop.

The omitted subject is understood as the speaker, so the sentence means something like:

• I slept on the bus and ended up missing my stop.
• While I was asleep on the bus, I passed my bus stop.

So the idea is not that the speaker walked past it, of course. It means they stayed on the bus and went beyond the stop.

Japanese often leaves things implied when they are obvious from context.

Here, バス停 just says bus stop, but in context it naturally means:

• the bus stop I was supposed to get off at
• my stop

A more explicit version could say something like:

• 降りるバス停を通り過ぎてしまいました
• 自分のバス停を通り過ぎてしまいました

But the original sentence is natural and concise.

Yes. Japanese often omits the subject when it is clear from context.

So the full idea is something like:

• 私はバスで寝ていて、バス停を通り過ぎてしまいました。

But 私は is unnecessary unless the speaker wants emphasis or contrast.

This is very normal in Japanese.

It mainly gives the background situation, and it also strongly suggests a reason/cause.

So the sentence feels like:

• Because I was asleep on the bus, I missed my stop.
• While I was sleeping on the bus, I went past the bus stop.

Japanese often uses the て-form this way without explicitly saying because.

Usually 寝ていて is better here.

〜ながら means while doing X, doing Y, and it is most natural when the same person is consciously doing two actions at once.

For example:

• 音楽を聞きながら勉強する = study while listening to music

But sleeping is not really a deliberate accompanying action in the same way. So:

• バスで寝ながら、バス停を通り過ぎた sounds less natural

寝ていて works better because it describes the state/background:

• while I was asleep...

Because the speaker is describing a completed event in the past, and the sentence is in polite style.

Breakdown:

• しまう = helper verb adding completion/regret
• しまいました = polite past form

So the whole sentence is politely saying something that already happened:

• I ended up passing/missing the bus stop.

A casual version would be:

• バスで寝ていて、バス停を通り過ぎてしまった。

And in casual speech, people often contract it further to:

• バスで寝ていて、バス停を通り過ぎちゃった。

A very natural understanding would be:

• I fell asleep on the bus and missed my stop.
• I was asleep on the bus and ended up going past my stop.

Even though the Japanese literally says something closer to passed the bus stop, the natural meaning is missed my stop.