Minua väsyttää, joten menen aikaisin nukkumaan.

Because väsyttää does not work like English I am tired.

In Finnish, väsyttää is an experiencer verb: it expresses a feeling that affects someone. The person who feels it is put in the partitive case, so:

• minua väsyttää = I feel tired / I’m sleepy
• literally something like tiredness is affecting me

So minua is the partitive form of minä.

Other similar patterns are:

• minua pelottaa = I’m scared
• minua nolottaa = I’m embarrassed
• minua janottaa = I’m thirsty

This is a very common Finnish pattern.

Väsyttää means to feel tired, to be sleepy, or more literally something makes one tired.

It is usually used in the 3rd person singular form:

• minua väsyttää
• sinua väsyttää
• häntä väsyttää

So the verb itself does not change according to the person here in the usual way. Instead, the person is shown by the object-like form:

• minua = me
• sinua = you
• häntä = him/her

This is why the structure feels unusual to English speakers.

Both can mean that someone is tired, but they are not exactly the same.

• minua väsyttää = I feel tired / sleepy
• olen väsynyt = I am tired

A useful rough distinction:

• väsyttää often focuses on the feeling happening right now, especially sleepiness
• väsynyt is an adjective, describing your state

So in this sentence, minua väsyttää, joten menen aikaisin nukkumaan, väsyttää fits very naturally because it leads to going to sleep early.

Because Finnish often leaves out personal pronouns when they are clear from the verb ending.

• menen already means I go / I’m going
• the ending -n shows 1st person singular

So:

• menen aikaisin nukkumaan = I’m going to sleep early

You can say minä menen, but it usually adds emphasis, contrast, or clarity.

For example:

• Minä menen, mutta hän jää. = I’m going, but he/she is staying.

In a normal neutral sentence, just menen is more natural.

Finnish often uses the present tense for the near future, especially when the context makes the timing clear.

So:

• menen aikaisin nukkumaan can mean I’m going to go to sleep early
• in natural English, that is often translated as I’ll go to bed early

This is very common in Finnish. You do not need a special future tense here.

Joten means so, therefore, or thus.

In this sentence:

• Minua väsyttää, joten menen aikaisin nukkumaan.
• I’m tired/sleepy, so I’m going to sleep early.

It connects the first clause and the result that follows.

It is slightly more formal or written-sounding than the very basic English so, but it is still common and natural.

Because after a verb of motion like mennä when you are going somewhere to do something, Finnish often uses the third infinitive illative.

So:

• mennä nukkumaan = to go to sleep / go to bed
• literally something like go into sleeping

Here:

• nukkua = to sleep
• nukkumaan = into sleeping / to sleep

This pattern is very common:

• mennä syömään = go eat
• mennä opiskelemaan = go study
• mennä uimaan = go swim

So mennä + verb in -maan/-mään is an important structure to learn.

Aikaisin means early.

In this sentence it modifies the action of going to sleep:

• menen aikaisin nukkumaan = I go to sleep early

Its position is quite natural here, but Finnish word order is flexible. You could also hear:

• menen nukkumaan aikaisin

Both are possible. The version in your sentence is very natural and clear.

No, they are related to sleep, but they are different things.

• nukkumaan = to sleep / to bed, as part of the action go to sleep
• sänkyyn = into bed
• nukkumaanmenoaika = bedtime

So:

• menen nukkumaan = I’m going to sleep / to bed
• menen sänkyyn = I’m going into bed

They can overlap in meaning, but they are not identical grammatically.

Not completely. Finnish word order is more flexible than English, although some versions sound more natural than others.

The original sentence:

• Minua väsyttää, joten menen aikaisin nukkumaan.

is a very normal, neutral way to say it.

Possible variation:

• Minua väsyttää, joten menen nukkumaan aikaisin.

This is also fine.

But word order can affect emphasis. Finnish often puts the most important or new information in a prominent position, so changing the order can slightly change the focus.

Yes, absolutely.

• Olen väsynyt, joten menen aikaisin nukkumaan.
• Minua väsyttää, joten menen aikaisin nukkumaan.

Both are natural.

The version with minua väsyttää may sound a little more like I feel sleepy / I’m feeling tired, while olen väsynyt is simply I am tired.

In this context, both work well.

Because Finnish and English build the idea differently.

English says:

• go to bed
• go to sleep

Finnish often uses the verb idea directly:

• mennä nukkumaan

So instead of naming the destination as bed, Finnish expresses the purpose or activity: go to sleep.

That is why a word-for-word translation can feel strange. It is better to learn mennä nukkumaan as a whole pattern.