sekkaku hayaku okitano ni, densya ga okurete gakkarisimasita

せっかく adds the feeling that someone made a special effort, but that effort did not pay off.

So here it is not just I woke up early. It is more like:

• I went to the trouble of waking up early
• I woke up early for once / on purpose
• I made the effort to wake up early, but...

That is why it works so naturally with のに later in the sentence. Together, they create the feeling of I did all that, and yet...

Because 早く is the adverb form of the -i adjective 早い.

• 早い = early / fast
• 早く = early / quickly

Since it modifies the verb 起きた (woke up), you need the adverb form:

• 早く起きた = woke up early

Using 早い directly before the verb would be ungrammatical here.

Because のに usually attaches to the plain form of a verb.

So:

• 起きたのに = even though I woke up
• not 起きましたのに in normal everyday speech

This is very common in Japanese: even in a polite sentence, a clause before a connector like のに, けど, から, etc. often uses the plain form.

Then the main sentence ends politely:

• がっかりしました

So the sentence mixes:

• plain form in the earlier clause: 起きた
• polite form at the end: しました

That is completely normal.

のに expresses contrary to expectation or even though / despite the fact that.

In this sentence:

• せっかく早く起きたのに = even though I made the effort to wake up early...

It often carries an emotional nuance, especially disappointment, frustration, or complaint.

So this is not just a neutral contrast. It sounds like:

• I woke up early, but it didn’t help
• Even though I woke up early, the train was delayed

In のに, the の is part of the grammar pattern. You should think of のに as one unit.

It attaches to the plain form of a clause:

• 行くのに
• 食べたのに
• 静かなのに
• 学生なのに

So here:

• 起きた + のに → 起きたのに

You do not normally separate it into 起きたに. That would be wrong.

All three can connect two ideas, but the nuance is different.

• けど / が = plain contrast, often neutral

  • 早く起きたけど、電車が遅れた
  • I woke up early, but the train was delayed

• のに = stronger feeling of unexpected result, often with disappointment or frustration

  • 早く起きたのに、電車が遅れた
  • Even though I woke up early, the train was delayed

In your sentence, のに is a better choice because the speaker is clearly upset that their effort was wasted.

There are two things happening here:

1. Why が?

電車 is the subject of 遅れて.

• 電車が遅れる = the train is delayed / runs late

So が marks the train as the thing that was late.

2. Why 遅れて?

This is the te-form of 遅れる.

Here the て-form connects this event to the next one:

• 電車が遅れて、がっかりしました
• The train was delayed, and I was disappointed

So the sequence is:

1. I woke up early
2. the train was delayed
3. I was disappointed

It can feel like both, depending on context.

Literally, て-form often just connects actions:

• the train was delayed, and...

But in real usage, it often also suggests the reason for what comes next:

• the train was delayed, so I was disappointed

In this sentence, the listener naturally understands that the train delay is the reason for the disappointment.

がっかりする is a very common expression meaning to be disappointed.

It behaves like a suru-verb:

• dictionary form: がっかりする
• past polite: がっかりしました
• plain past: がっかりした

So:

• がっかりしました = was disappointed / got disappointed

Even though がっかり looks a bit like a sound-symbolic or mimetic word, as an expression it is very standard and common.

The subject is omitted because Japanese often leaves out information that is clear from context.

Here, the natural understanding is:

• I woke up early
• I was disappointed

So the full idea is something like:

• I made the effort to wake up early, but the train was delayed, so I was disappointed.

Japanese often does this when the speaker is obviously talking about their own experience.

It strongly suggests that, yes.

The combination of:

• せっかく = I made a special effort
• 早く起きた = woke up early
• のに = but in spite of that
• 電車が遅れて = the train was delayed

makes it sound like the early wake-up was meant to help with travel or timing, but the train delay ruined the plan.

Even if that purpose is not stated directly, it is easy to infer.

Yes, but the nuance would change.

Without せっかく:

• 早く起きたのに、電車が遅れてがっかりしました。

This still means:

• Even though I woke up early, the train was delayed, and I was disappointed.

But with せっかく, the sentence more strongly emphasizes:

• I made an effort
• it feels like a waste
• the disappointment is stronger

So せっかく adds emotional weight.

The comma marks a pause between the two parts of the sentence:

• せっかく早く起きたのに、
• 電車が遅れてがっかりしました

It helps readability and reflects the natural break after the even though... part.

It is not absolutely required in all writing, but it is very natural here.

Yes, it is natural.

A very natural interpretation is:

• I made the effort to get up early, but the train was delayed, and I was disappointed.

The flow is good because:

• せっかく sets up effort
• のに sets up the disappointing contrast
• 電車が遅れて gives the bad event
• がっかりしました gives the emotional result

So this is a good example of how Japanese expresses effort + bad outcome + disappointment.