Мне пришлось взять больничный из-за высокой температуры.

Because пришлось is used in an impersonal construction.

The verb прийтись / приходиться in this meaning means to have to, to be forced to, to end up needing to. In Russian, the person who is affected is usually put in the dative case, not the nominative.

So:

• мне пришлось = I had to
• literally something like to me, it became necessary

That is why you get:

• мне = to me
• тебе = to you
• ему / ей = to him / her

Examples:

• Мне пришлось уйти. = I had to leave.
• Ей пришлось ждать. = She had to wait.

Not exactly.

Пришлось means something like:

• had to
• was forced to
• ended up having to

It often suggests that the situation made it necessary, sometimes against the speaker’s preference.

By contrast, я должен был means I was supposed to / I was obliged to / I had to in a more direct, personal-obligation sense.

Compare:

• Мне пришлось взять больничный.
  = I had to take sick leave.
  The circumstances forced it.

• Я должен был взять больничный.
  = I was supposed to take sick leave / I ought to have taken sick leave.
  This can sound more like duty, expectation, or advice.

So пришлось is very natural here because a high fever created the necessity.

Because this is an impersonal sentence.

In Russian, impersonal past-tense predicates often appear in the neuter singular form:

• пришлось
• удалось
• хотелось
• нужно было etc.

There is no normal grammatical subject like я controlling the verb form. The person is in the dative (мне), so the verb stays in the default impersonal past form: -лось.

That is why it is:

• Мне пришлось... not
• Мне пришёлся... not
• Я пришёл...

Idiomatic meaning: to take sick leave or to go on sick leave.

Literally:

• взять = to take
• больничный = a sick note / sick leave document / sick leave

In everyday Russian, больничный is often a shortened noun from больничный лист.

So:

• взять больничный = to take sick leave
• sometimes also understood as to get a doctor’s sick note

Depending on context, it can refer to:

1. the official medical note, or
2. the period of leave itself.

In this sentence, it most naturally means I had to take sick leave.

Yes, historically it is an adjective, but in modern Russian it is very commonly used as a noun.

This is a common pattern in Russian: an adjective can stand alone when the noun is understood.

Here:

• больничный (лист) = sick leave certificate / doctor’s note

The noun лист is omitted because it is obvious from context.

Similar shorthand exists in Russian in other expressions too, where an adjective becomes a noun in everyday usage.

So learners should simply recognize больничный here as a standard noun meaning sick leave or sick note.

Because взять is perfective, and here the sentence refers to a completed single action: the speaker had to take sick leave.

Compare the aspects:

• брать = imperfective, process / repeated / general
• взять = perfective, one completed act

In this sentence, the focus is on the fact that the action happened as a whole:

• Мне пришлось взять больничный.
  = I had to take sick leave.

If you used брать, it would sound less natural here unless the context specifically emphasized process or repetition.

After из-за in the meaning because of, Russian uses the genitive case.

So:

• из-за = because of / due to
• высокая температура = high temperature / fever
• genitive form: высокой температуры

Breakdown:

• высокая → высокой
• температура → температуры

So:

• из-за высокой температуры = because of a high fever / due to a high temperature

Yes, it is a very normal Russian way to say fever.

Russian often uses температура where English would more naturally say a fever.

So:

• У меня температура. = I have a fever.
• высокая температура = a high fever / high temperature

A very literal translation into English may sound slightly stiff, but in Russian this is completely natural.

Из-за means because of, due to, and often points to a cause.

In this sentence it is the most natural choice:

• из-за высокой температуры = because of a high fever

Other expressions are possible in Russian, but they can differ in style:

• по причине высокой температуры = due to high fever
  More formal, less conversational.

• из-за того, что была высокая температура = because there was a high fever
  More explicit, but longer.

So из-за is concise and idiomatic here.

Yes. Russian word order is flexible, though the emphasis changes.

Original:

• Мне пришлось взять больничный из-за высокой температуры.

Possible variants:

• Из-за высокой температуры мне пришлось взять больничный.
• Больничный мне пришлось взять из-за высокой температуры.

All are grammatical. The original is neutral and natural.

Very roughly:

• putting из-за высокой температуры first emphasizes the reason
• putting больничный earlier emphasizes what had to be taken

Russian uses word order more for focus and emphasis than for basic grammar.

Yes, potentially. Больничный can refer either to:

• the official sick-leave document, or
• the sick leave itself

In many real contexts, both ideas overlap: you get the medical note in order to go on sick leave.

So the sentence may suggest:

• I had to take sick leave or
• I had to get a sick note

Usually context tells you which is more important. If no extra context is given, take sick leave is the safest natural translation.

It is neutral and very natural modern Russian.

Parts of it are especially common in everyday speech:

• мне пришлось = very common
• взять больничный = standard everyday phrase
• из-за высокой температуры = neutral

So this sentence works well in normal conversation, messages, or everyday narration. It is not slang, but it is not overly formal either.