yoru ni seki wo suruto, nemurenaikoto ga arimasu.

に marks a point in time here, so 夜に means at night.

Japanese often uses に with time expressions, especially when the speaker wants to clearly mark when something happens. In this sentence, 夜にせきをすると means when/if I cough at night.

A learner may notice that some time words do not always need に. That is true, but 夜に is very natural and clear here.

In Japanese, せき is a noun meaning cough, and する turns it into an action: せきをする = to cough.

This noun + を + する pattern is very common:

• 勉強をする = to study
• 運動をする = to exercise
• せきをする = to cough

Japanese also has other ways to express coughing, such as せきが出る, which means something like a cough comes out or I start coughing. That version can sound a little more involuntary. せきをする is a straightforward way to say to cough.

Here, と is not the and particle. It is a conditional marker meaning something like:

• when
• if
• whenever

So:

• せきをすると = when/if I cough

This と is often used when the second part is a natural result, usual result, or repeated result of the first part.

So the sentence has the feeling of: When I cough at night, there are times when I can’t sleep.

Because と connects to the plain form of the verb.

The plain form here is する, so:

• する + と → すると

That does not mean the single word すると in the sense of and then. In this sentence, it is simply:

• せきをする
  • と

So the structure is:

• 夜に
• せきをする
• と
• 眠れないことがあります

眠れない means cannot sleep or am unable to sleep, not just do not sleep.

It comes from 眠る = to sleep, and 眠れる is the potential form, meaning can sleep. So:

• 眠れる = can sleep
• 眠れない = cannot sleep

This is different from simply choosing not to sleep.

So in this sentence, the meaning is not I don’t sleep, but I can’t sleep.

ことがあります means there are times when... or sometimes...

So:

• 眠れないことがあります = there are times when I can’t sleep
• more naturally in English: I sometimes can’t sleep

The こと turns the whole clause 眠れない into a noun-like idea:

• the fact/event of not being able to sleep

Then があります literally says that such occasions exist.

This is a very common Japanese pattern:

• verb/plain clause + ことがある

It is ことがある because the whole event is treated as the thing that exists.

In Japanese, with ある, the thing that exists is commonly marked by が.

So here:

• 眠れないこと = the event/fact of not being able to sleep
• がある = exists / happens

Together:

• 眠れないことがあります = there are times when I can’t sleep

The subject is omitted, which is very normal in Japanese.

The sentence itself does not explicitly say I, you, or they. The listener understands it from context. In many everyday situations, this would naturally mean I:

• When I cough at night, I sometimes can’t sleep.

If the surrounding conversation were about someone else, it could refer to that person instead.

Not necessarily.

By itself, A と B often suggests a natural or regular result: when A happens, B happens. But here the second half is 眠れないことがあります, which weakens it and makes it sometimes rather than always.

So the overall meaning is closer to:

• When I cough at night, I sometimes can’t sleep not
• Every time I cough at night, I definitely can’t sleep

No. Normal Japanese writing does not use spaces between words.

This sentence would usually be written like this:

夜にせきをすると、眠れないことがあります。

In learning materials, spaces are often added to help beginners see the parts of the sentence.

Yes. せき can be written as 咳.

So the sentence could also be written:

夜に咳をすると、眠れないことがあります。

However, words like 咳 are often written in hiragana in beginner materials, and even native materials may sometimes prefer kana depending on style and readability.