Bekleme odasında on dakika kestirdim, çünkü gece hiç uyuyamadım.

Bekleme odası means waiting room.

• bekleme comes from beklemek and means waiting
• oda means room
• oda-sı is the compound form used in expressions like waiting room

Then -nda adds the meaning in / at.

So:

• bekleme odası = waiting room
• bekleme odasında = in the waiting room

The reason it is -nda instead of just -da is that odası already has the compound/possessive-type ending -sı, so the locative comes after that: oda-sı-nda.

Because on dakika is a duration expression: for ten minutes.

In Turkish, lengths of time often appear as a bare number + time word, without a case ending:

• iki saat bekledim = I waited for two hours
• üç gün kaldım = I stayed for three days
• on dakika kestirdim = I napped for ten minutes

English needs for, but Turkish usually does not.

Here kestirdim means I took a quick nap / I dozed off briefly.

It is close to uyudum (I slept), but not exactly the same:

• uyudum = I slept
• kestirdim = I slept briefly, lightly, or had a short nap

So kestirdim gives a more specific nuance: this was not a full normal sleep, just a short bit of sleep.

Yes, it can.

This is a very useful thing to notice: kestirmek has different meanings depending on context.

For example:

• Saçımı kestirdim. = I had my hair cut.
• Biraz kestirdim. = I took a short nap.

In your sentence, because the context is being tired and not sleeping at night, the meaning is clearly to nap / doze.

It breaks down like this:

• kestir- = verb stem
• -di- = past tense
• -m = I

So kestirdim = I napped / I dozed

The past tense appears here as -di because of normal sound and vowel harmony rules.

This is an important difference.

• uyumadım = I didn’t sleep
• uyuyamadım = I couldn’t sleep

So the sentence is not just saying that sleep did not happen. It says the speaker was unable to sleep.

A simple breakdown is:

• uyu- = sleep
• -ya- / -a- = part of the inability pattern
• -ma- = negative
• -dı = past
• -m = I

So uyuyamadım means I was unable to sleep.

With a negative verb, hiç usually means at all.

So:

• uyuyamadım = I couldn’t sleep
• hiç uyuyamadım = I couldn’t sleep at all

It strengthens the negative idea.

In other contexts, hiç can mean things like ever or never, but here the best sense is at all.

Turkish often uses time words by themselves as adverbs, without adding a case ending.

So gece here means something like:

• at night
• during the night
• and in this past context, often naturally understood as last night

That is why gece works without -de.

If the speaker wanted to be more explicit, they could say dün gece for last night. But in context, gece already sounds natural.

Çünkü means because and introduces the reason.

A very common pattern is:

• result, çünkü reason

That is exactly what happens here: first the speaker says what they did, then gives the reason.

You usually can change ideas around in Turkish, but with çünkü, putting the reason second is the most natural pattern. If you want the reason first, Turkish often prefers -dığı için instead:

• Gece hiç uyuyamadığım için, bekleme odasında on dakika kestirdim.

That means essentially the same thing, but starts with the reason.

Because the sentence has two full clauses:

• Bekleme odasında on dakika kestirdim
• gece hiç uyuyamadım

When çünkü connects two full clauses, a comma is very commonly used before it in Turkish writing.

So the comma helps show the pause and the relationship between the main statement and the reason.