tukarete ita node, densya de nete oriru eki wo norisugosite simaimasita.

疲れていた is the past progressive/state form of 疲れる.

Here it means something like:

• I was tired
• I had become tired and was in that state

By contrast, 疲れた often means got tired or was tired in a simpler way, but 疲れていた emphasizes the ongoing condition at that time.

So in this sentence, 疲れていたので naturally sets up the background:

• Because I was tired...

ので means because, since, or as.

In this sentence:

• 疲れていたので = because I was tired

Compared with から, ので often sounds:

• a bit softer
• more explanatory
• slightly more formal or neutral

So:

• 疲れていたから = also correct, a bit more direct
• 疲れていたので = sounds smoother and more like giving a reason calmly

Japanese often leaves out subjects when they are obvious from context.

Here, the person who was tired, slept, and missed the station is understood to be the speaker, so 私 is unnecessary.

A natural English translation needs I, but Japanese does not.

So the sentence is understood as:

• (I) was tired, so (I) fell asleep on the train and missed my stop.

Here 電車で means on the train or in the train.

The particle で can mark:

• the place where an action happens
• the means/method by which something is done

In this sentence, 寝て happens in/on the train, so で marks the location of the action:

• 電車で寝て = sleeping on the train

Even though English says on the train, Japanese uses で, not a direct equivalent of on.

寝て is the て-form of 寝る.

Here it links actions together:

• 電車で寝て
• 降りる駅を乗り過ごしてしまいました

So the flow is:

• I slept on the train, and as a result I missed the station where I should get off.

The て-form often connects actions in sequence, especially when one action leads into another.

降りる駅 means:

• the station where I get off
• the station I am supposed to get off at

This is a relative clause: 降りる directly modifies 駅.

Japanese often uses the dictionary form in this kind of phrase when describing a usual, intended, or relevant action:

• 読む本 = the book I read / will read
• 行く店 = the store I go to / will go to
• 降りる駅 = the station where I get off

If you said 降りた駅, that would mean:

• the station where I got off

But in this sentence, the point is that the speaker did not get off there, so 降りた駅 would not fit.

This is a very common question.

The verb 乗り過ごす means:

• to go past
• to miss (a stop/station by staying on the train too long)

With this verb, the stop or station that gets missed is marked by を:

• 駅を乗り過ごす
• 停留所を乗り過ごす

This is just how the verb works grammatically in Japanese.

So even though English might say:

• miss the station
• go past the station

Japanese uses を because the station is treated as the object of 乗り過ごす.

しまう adds a nuance that the action was:

• completed fully, and/or
• unfortunate
• accidental
• regrettable

So:

• 乗り過ごしました = I missed the station
• 乗り過ごしてしまいました = I ended up missing the station / unfortunately missed the station

In this sentence, しまいました strongly suggests:

• it was not intentional
• the speaker regrets it

That matches the situation very well.

The main event of the sentence happened in the past, so the sentence ends in past tense:

• 乗り過ごしてしまいました = ended up missing

It is also in polite style because of -ました.

Notice the timeline:

• 疲れていた = was tired
• 寝て = slept
• 乗り過ごしてしまいました = missed the station

All of these describe past events, and the final verb carries the main tense and politeness of the sentence.

Literally, 寝る means to sleep, but in this context 電車で寝て often feels like:

• I fell asleep on the train
• I was sleeping on the train

Because the result was that the speaker missed their station, English often translates it as fell asleep, which sounds more natural.

So the Japanese itself does not explicitly say fall asleep in a separate way, but the context strongly suggests that meaning.

Yes, in this sentence 降りる駅 is essentially:

• the station where I was supposed to get off
• my stop

Japanese often describes things more literally than English.

So instead of a single phrase like my stop, Japanese says:

• 降りる駅 = the station to get off at

That is a very natural Japanese way to express it.

A helpful breakdown is:

• 疲れていたので、
  Because I was tired,

• 電車で寝て
  I slept / fell asleep on the train,

• 降りる駅を
  the station where I was supposed to get off

• 乗り過ごしてしまいました。
  I ended up missing / going past.

So the basic logic is:

1. background reason: I was tired
2. action: I slept on the train
3. result: I missed my stop

This kind of reason → action → result structure is very common in Japanese.