Ana se simte obosită.

Because the Romanian verb here is a se simți, which is the usual way to say to feel in the sense of physical or emotional condition.

So:

• a simți = to feel / to sense something
  
  • Simt frigul. = I feel the cold.
• a se simți = to feel a certain way
  
  • Mă simt bine. = I feel well.

In Ana se simte obosită, se is the reflexive pronoun used with the 3rd person singular.

Simte is the 3rd person singular present tense form of a simți / a se simți.

That means it goes with subjects like:

• el = he
• ea = she
• a singular name like Ana

So:

• Eu mă simt = I feel
• Tu te simți = you feel
• Ana se simte = Ana feels
• El se simte = he feels

Because obosită agrees with Ana, which is feminine singular.

In Romanian, adjectives usually agree in gender and number with the noun or person they describe.

Here:

• obosit = masculine singular
• obosită = feminine singular
• obosiți = masculine plural / mixed plural
• obosite = feminine plural

So:

• Mihai se simte obosit.
• Ana se simte obosită.

Yes. Ana este obosită is also correct.

The difference is mainly one of focus:

• Ana este obosită = Ana is tired
• Ana se simte obosită = Ana feels tired

The version with se simte emphasizes Ana’s felt condition or experience. The version with este simply states the condition.

In many everyday situations, both are natural.

It is an adjective.

In this sentence, it functions as a predicative adjective: it describes the subject Ana after the verb phrase se simte.

So Romanian works similarly to English here:

• Ana feels tired
• tired describes Ana

Likewise:

• Ana se simte fericită. = Ana feels happy.
• Ana se simte rău. = Ana feels bad.

In a simple sentence like this, se normally goes before the conjugated verb:

• Ana se simte obosită.

That is the standard word order.

With negation, nu comes before the reflexive pronoun:

• Ana nu se simte obosită.

So the common order is:

subject + nu + reflexive pronoun + verb + adjective

You add nu before se:

• Ana nu se simte obosită. = Ana does not feel tired.

That is the normal Romanian placement.

Compare:

• Ana se simte obosită.
• Ana nu se simte obosită.

You change both the reflexive pronoun and the verb form.

Present tense of a se simți:

• eu mă simt = I feel
• tu te simți = you feel
• el/ea se simte = he/she feels
• noi ne simțim = we feel
• voi vă simțiți = you all feel
• ei/ele se simt = they feel

Examples:

• Mă simt obosit. = I feel tired.
  If the speaker is female: Mă simt obosită.
• Ne simțim obosiți. = We feel tired.
• Ele se simt obosite. = They feel tired.

Not in the way English speakers usually understand reflexive.

In Romanian, many verbs are used with reflexive pronouns as part of their normal form. A se simți is one of them. In this sentence, se does not really mean herself in a strong literal sense.

So you should usually learn a se simți as a whole expression meaning to feel.

A very literal English translation like Ana feels herself tired would sound unnatural. The natural meaning is simply Ana feels tired.

Ana se simte obosită is the normal, neutral order.

Romanian does allow some flexibility, but changes usually add emphasis or sound more literary, marked, or context-dependent. For a learner, the safest pattern is:

Subject + reflexive pronoun + verb + adjective

So it is best to stick with:

• Ana se simte obosită.

The final ă is a very common Romanian vowel. It is a short, neutral sound, similar to the a sound in English sofa for many speakers.

So obosită ends with that reduced vowel sound, not with a strong ah.

A rough pronunciation guide:

• obosită ≈ oh-bo-SEE-tuh

Not exact English spelling, but close enough to help.

Because obosită is not a noun here; it is an adjective describing Ana’s condition.

Romanian does not use an article before a predicative adjective in sentences like this.

So:

• Ana se simte obosită.
• Ana este fericită.

That is normal. You would not add an article before obosită here.

Yes.

Without se, a simți usually means to feel, to sense, or to perceive something directly.

Examples:

• Simt durere. = I feel pain.
• Simt miros de fum. = I smell smoke / I sense the smell of smoke.

With se, a se simți usually means to feel in a certain state:

• Mă simt bine. = I feel well.
• Ana se simte obosită. = Ana feels tired.

So both exist, but they are used differently.