Learn Hardcore Indonesian: Saya merasa gelisah, jadi saya sulit konsentrasi membaca buku malam ini. - I feel restless, so I find it hard to concentrate on reading a book tonight.

sehingga – more formal, also means so / such that.
Saya merasa gelisah sehingga saya sulit konsentrasi…
makanya – colloquial, like that’s why / so in speech.
Saya merasa gelisah, makanya saya sulit konsentrasi…

In neutral everyday Indonesian, jadi is very common and natural.

Why use merasa gelisah instead of just gelisah? What’s the difference?

Both are correct:

Saya merasa gelisah.
Saya gelisah.

Meaning is practically the same: I feel anxious / restless.

Nuance:

Saya merasa gelisah – slightly more explicit, literally I feel anxious; sounds a bit more formal or reflective.
Saya gelisah – more direct: I am anxious / restless; very natural in conversation.

You can freely use Saya gelisah, jadi saya sulit konsentrasi… as well.

Can konsentrasi be used as a verb like this? Why not berkonsentrasi?

Yes. In Indonesian, some nouns can function like verbs, and konsentrasi is one of them.

All of these are acceptable and common:

sulit konsentrasi
sulit untuk konsentrasi
sulit berkonsentrasi
sulit untuk berkonsentrasi

Nuance:

sulit konsentrasi – simple, very common in spoken Indonesian.
sulit berkonsentrasi – a bit more formal/standard; often used in writing.

There is no big meaning difference; it’s mainly style and formality.

Why is it sulit konsentrasi membaca buku, without untuk? Should it be sulit untuk konsentrasi membaca buku?

Both are possible:

sulit konsentrasi membaca buku – very natural, especially in speech.
sulit untuk konsentrasi membaca buku – also correct; slightly more formal or careful.

Structure:

sulit + [verb/verb phrase] is very common:
sulit tidur, sulit bicara, sulit fokus, sulit konsentrasi.

Adding untuk often makes the phrase sound a bit more formal or explanatory, but it is not required.

What’s the difference between sulit, susah, and sukar?

All can mean difficult / hard, but there are nuances:

sulit
- Neutral, slightly formal.
- Very common in both speech and writing.
- Good default: saya sulit konsentrasi.
susah
- More colloquial and emotional, sometimes closer to troublesome / causing problems.
- Saya susah konsentrasi is common in casual speech.
sukar
- Quite formal or literary.
- More likely in formal texts: masalah yang sukar diatasi.

In this sentence, sulit is the most natural neutral choice.

What does gelisah exactly mean? Is it more like anxious, nervous, or restless?

Gelisah covers several English ideas:

restless: can’t sit still, mind or body won’t calm down.
anxious / uneasy: inner worry, tension.
sometimes fidgety / agitated.

Compared to other words:

cemas – anxious, worried, usually about something specific or serious.
khawatir – worried, concerned.
gugup – nervous, often in a performance or social situation (stage fright, interviews).

Gelisah focuses on the uneasy, restless feeling, not always tied to a clear reason.

Why say membaca buku instead of just membaca? Isn’t reading already about books?

You can say either:

sulit konsentrasi membaca
sulit konsentrasi membaca buku

Both are grammatical.

Membaca buku is a bit more specific and concrete: it tells you what is being read. In real life, membaca could be about books, articles, messages, etc., so adding buku makes the picture clearer.

In everyday speech, people often still include buku, even if it feels a bit redundant in English.

Why malam ini and not ini malam? Are both possible?

The normal word order is:

time word + ini / itu
→ malam ini (this evening/tonight), kemarin malam (last night), etc.

Ini malam is not used with the meaning this evening / tonight. It would either sound wrong or be interpreted in a different, unnatural way.

Correct patterns:

malam ini – this evening / tonight (future or current evening).
tadi malam – last night (already past).

So for tonight, always use malam ini, not ini malam.

Could the sentence start with the result instead: Saya sulit konsentrasi membaca buku malam ini, karena saya merasa gelisah?

Yes, that is perfectly correct:

Saya sulit konsentrasi membaca buku malam ini, karena saya merasa gelisah.

This version uses karena (because) instead of jadi (so), and it flips the order:

Original: cause → effect
I feel anxious, so I find it hard to concentrate.
Alternative: effect → cause
I find it hard to concentrate because I feel anxious.

Both structures are natural.
With jadi, you normally put the cause first; with karena, you can put the effect first or the cause first.

Can I drop saya entirely and say Merasa gelisah, jadi sulit konsentrasi membaca buku malam ini?

In very casual spoken language, you might hear something like:

Merasa gelisah, jadi sulit konsentrasi membaca buku malam ini.

Listeners will still understand that I am the subject from context.

However:

In standard, careful Indonesian (especially writing), you should keep saya (or another subject) at least once, e.g.:
Saya merasa gelisah, jadi sulit konsentrasi…
Dropping the subject in both clauses makes the sentence sound incomplete or overly informal in writing.

So for learners and for clear, correct Indonesian, keep saya at least once.

Is there any tense marking here, or does malam ini handle all the time information?

Indonesian does not have verb tenses like English (no verb changes for past/present/future).

Time is usually shown by:

time expressions: malam ini (tonight), kemarin (yesterday), besok (tomorrow), tadi malam (last night), etc.
optional aspect words: sedang (in the middle of doing), sudah (already), akan (will).

Your sentence:

Saya merasa gelisah, jadi saya sulit konsentrasi membaca buku malam ini.

is understood as about tonight simply because of malam ini. You do not need to change the verbs or add any extra tense marker.