Learn Hardcore Finnish: Onpa vaikeaa nukahtaa heti, kun aivot pyörivät vielä pelin takia. - How hard it is to fall asleep immediately when the brain is still spinning because of the game.

On vaikeaa nukahtaa heti… = “It is hard to fall asleep right away…”
Onpa vaikeaa nukahtaa heti… = “It’s so hard to fall asleep right away…” (more expressive, a bit exclamatory or complaining)

It isn’t slang; it’s standard Finnish, just more “colored” than plain on.

Why is it vaikeaa and not vaikea?

Vaikeaa is the partitive form of vaikea (“difficult, hard”).

In Finnish, when you say that doing something is difficult, the adjective is typically in the partitive, and the action is an infinitive:

On vaikeaa nukahtaa. = “It is difficult to fall asleep.”
On helppoa puhua. = “It is easy to speak.”

Grammar-wise:

The “thing that is difficult” is the whole action nukahtaa heti, kun aivot…
In sentences like this, Finnish usually uses the partitive predicative (vaikeaa) with an infinitive “subject”.

You can see on vaikea in other contexts (especially with a concrete noun):

Tämä on vaikea tehtävä. = “This is a difficult task.”

But with an action (to do something), on vaikeaa + infinitive is the natural pattern:

On vaikeaa nukahtaa heti. (not on vaikea nukahtaa heti in normal speech/writing)

What is the difference between nukahtaa and nukkua here?

nukkua = “to sleep” (be in the state of sleeping)
nukahtaa = “to fall asleep” (the moment of starting to sleep)

So:

On vaikeaa nukkua. = “It is hard to sleep.” (staying asleep is difficult)
On vaikeaa nukahtaa. = “It is hard to fall asleep.” (getting to sleep is difficult)

In this sentence, the person is talking about the process of falling asleep, so nukahtaa is the correct verb.

What does heti, kun mean, and is it the same as heti kun?

Heti kun is a fixed combination meaning roughly:

“as soon as”
“right when”

In your sentence:

nukahtaa heti, kun aivot pyörivät…
= “to fall asleep right away when the brain is still spinning…”

Written out fully, you can think of it as heti kun (“as soon as / right when”), but Finnish punctuation puts a comma between the main clause and the kun-clause:

Onpa vaikeaa nukahtaa heti, kun aivot pyörivät vielä pelin takia.

So:

Logically: heti kun
On the page: …heti, kun… because kun introduces a separate clause.

Why is there a comma before kun?

In standard Finnish punctuation, you usually put a comma between a main clause and a subordinate clause introduced by kun:

Lähden kotiin, kun työpäivä loppuu.
“I’ll go home when the workday ends.”

Same here:

Main clause: Onpa vaikeaa nukahtaa heti
Subordinate clause with kun: kun aivot pyörivät vielä pelin takia

So you get:

Onpa vaikeaa nukahtaa heti, kun aivot pyörivät vielä pelin takia.

Even though heti kun functions together in meaning (“as soon as”), punctuation still respects the clause boundary.

Why is aivot plural if English says “brain” (singular)?

In Finnish, aivot (“brain”) is inherently plural—you almost always see it in the plural form, even when talking about one person’s brain:

Minun aivot = “my brain”
Hänen aivonsa = “his/her brain”
Aivot ovat väsyneet. = “(My) brain is tired.”

So:

aivot pyörivät literally: “the brains are spinning”
Natural English: “the brain is spinning” / “my mind is racing”

It’s a quirk of Finnish: some body parts are typically plural (like aivot, kasvot “face”).

Why is the verb pyörivät (plural) and not pyörii?

Because aivot is grammatically plural, the verb agrees with it in the 3rd person plural:

aivot pyörivät
- aivot = plural subject (“brains”)
- pyörivät = 3rd person plural of pyöriä (“to spin”)

So the standard written form is:

aivot pyörivät

In spoken colloquial Finnish, many people say:

aivot pyörii (singular verb with a plural subject)

That’s very common in speech, but in neutral written Finnish, you should match number:

aivot pyörivät (correct standard)
aivot pyörii (colloquial speech)

What does vielä add here? Could you leave it out?

Vielä here means still:

aivot pyörivät vielä = “the brain is still spinning”

It emphasizes that the mental activity is continuing, even though you’re trying to sleep.

If you leave vielä out:

aivot pyörivät pelin takia = “the brain is spinning because of the game”

That’s grammatically fine, but slightly weaker: you lose the nuance that this spinning is still going on at the time when you want to fall asleep. So vielä adds a sense of ongoing, not-yet-stopped activity.

What does pelin takia mean, and why is it pelin and not peli?

peli = “game” (basic form)
pelin = genitive singular of peli
takia = postposition meaning “because of / due to”

Together:

pelin takia = “because of the game” / “on account of the game”

Postpositions like takia usually require the preceding noun to be in the genitive case:

sateen takia = “because of the rain”
sinun takiasi = “because of you”
pelin takia = “because of the game”

So pelin must be genitive here; peli takia would be ungrammatical.

Could you use something else instead of pelin takia, like pelin vuoksi? Is there a difference?

Yes, you could say:

aivot pyörivät vielä pelin vuoksi

Varten / vuoksi / takia all express reason/purpose but with slightly different flavors:

pelin takia – very common, neutral “because of the game”
pelin vuoksi – a bit more formal or “bookish”, but also means “because of the game”
peliä varten – usually “for the game” in the sense of purpose (e.g. “prepared for the game”)

In your sentence, both pelin takia and pelin vuoksi would be understood the same: “because of the game.” Takia is the most everyday, natural choice here.

Is the word order fixed, or could you say this sentence in another way?

Finnish word order is flexible. You can move elements around for emphasis or style. For example:

Kun aivot pyörivät vielä pelin takia, onpa vaikeaa nukahtaa heti.
- Subordinate clause first; sounds a bit more formal or “written style”.
Onpa vaikeaa heti nukahtaa, kun aivot pyörivät vielä pelin takia.
- Moves heti closer to nukahtaa, focusing on “immediately falling asleep”.
On vaikeaa nukahtaa heti, kun aivot vielä pyörivät pelin takia.
- Drops -pa, making it less exclamatory.

All are grammatically fine; the original is a natural, conversational order. The main rules to respect are:

verbs and their infinitives stay together (vaikeaa nukahtaa),
the kun-clause stays intact,
pelin takia stays attached to what it semantically modifies (pyörivät).

Could you just say On vaikeaa nukahtaa heti, kun aivot pyörivät vielä pelin takia without -pa? Does it change the meaning?

Yes, you can:

On vaikeaa nukahtaa heti, kun aivot pyörivät vielä pelin takia.

This is fully correct. Dropping -pa removes the emotional/exclamatory nuance and makes the sentence more neutral, almost like a simple statement of fact.

Compare:

On vaikeaa nukahtaa heti… = “It is hard to fall asleep right away…” (neutral)
Onpa vaikeaa nukahtaa heti… = “It’s so hard to fall asleep right away…” (more feeling, emphasis, often with mild frustration or surprise)

What exactly does kun mean here? Is it “when” or “because”?

In this sentence, kun is primarily “when”:

…nukahtaa heti, kun aivot pyörivät…
= “…to fall asleep right away when the brain is still spinning…”

So it marks a time condition: at the time that the brain is still spinning, it’s hard to fall asleep.

However, Finnish kun can sometimes also imply a mild causal sense (“since / because”), depending on context and intonation. Here, English might naturally translate the overall idea as:

“It’s so hard to fall asleep right away, when your brain is still spinning because of the game.”
“It’s so hard to fall asleep right away if your brain is still spinning because of the game.”

But grammatically, this is the time/condition use of kun, not the explicit causal conjunction koska (“because”).