Learn Hardcore Japanese: kanozyo ha hirune wo sinai to guai ga waruku naru mitai. - If she doesn’t take a nap, she seems to feel unwell.

Here it’s the conditional “if (she) doesn’t (nap).” So the whole clause is “If she doesn’t take a nap, she seems to feel unwell.” It is not the “have to” usage. Note: In casual speech, standalone 〜ないと can be short for obligation (〜ないといけない), e.g., 宿題しないと。 = “I gotta do my homework.” But in this sentence, because there’s a result clause after it, it’s the literal “if not … then …” conditional.

Why use the conditional particle と instead of たら, なら, or なければ?

と marks a natural, automatic, or habitual consequence: “whenever/if A, then B (inevitably/typically).”

昼寝をしないと具合が悪くなる: whenever she skips a nap, she tends to feel unwell. (habitual/automatic)
昼寝をしなかったら具合が悪くなる: if she didn’t nap (on that occasion), she would/will feel unwell. (more event-specific)
昼寝をしなければ具合が悪くなる: “if she does not,” slightly more formal/literary.
昼寝をしないなら: “if it’s the case that she doesn’t (nap),” conditional on a premise, not a natural law.

What nuance does みたい add? How is it different from ようだ, らしい, and そうだ?

みたい: casual “seems/looks like,” often based on the speaker’s sense/observation. Very conversational.
ようだ: similar meaning but more neutral/formal than みたい.
らしい: often hearsay (“I hear that...”), or “typical of” (彼は先生らしい = “he’s teacher-like”).
そうだ: two uses:
- hearsay: 〜だそうだ (“I hear that…”),
- appearance/prediction: 寒そうだ (“looks cold”), 雨が降りそうだ (“looks like it’ll rain”). Here, みたい softens the claim to “it seems (to me)” rather than stating it as a hard fact.

Why is there no だ after みたい? Is みたいだ or みたいです better?

In casual speech, sentence-final だ after みたい is often dropped: …みたい。 Adding だ/です is more complete/polite:

Casual: …みたい。
Neutral: …みたいだ。
Polite: …みたいです。

What’s the function of は on 彼女は and が on 具合が? Why not 具合は?

彼女は sets the topic: “as for her…”
具合が悪い is a fixed pattern; が marks the thing that has the property (the condition/health). Saying 具合は悪い is possible but adds contrast (“as for her condition, it’s bad”), which is not needed here.

Why is it 悪くなる and not 悪いになる?

With i‑adjectives, use the adverbial form (〜く) before なる to express “become X”:

悪い → 悪くなる (become bad/unwell) With na‑adjectives, use 〜に:
元気 → 元気になる (become energetic)

Can I drop the を in 昼寝をしない? Is 昼寝しない okay?

Yes. する-nouns (like 昼寝, 勉強, 散歩) can appear as Xをする or just Xする. Both are correct; the version without を feels a bit more casual:

昼寝をしない and 昼寝しない both mean “don’t take a nap.”

What’s the difference between 具合が悪くなる, 気分が悪くなる, and 体調が悪くなる?

具合が悪くなる: general “feel unwell,” broad and common.
気分が悪くなる: “feel sick/queasy/dizzy,” also “feel bad (mood),” context-dependent.
体調が悪くなる: “one’s physical condition deteriorates,” slightly more formal/medical.

Does the sentence mean a one-time future event, or a general tendency?

With と + non-past, it usually states a general/habitual tendency. So it means “She tends to get unwell if she doesn’t nap,” not just a single future instance.

Is 彼女 natural here? Could it mean “girlfriend”?

彼女 can mean “she” or “girlfriend.” Whether it sounds natural depends on context.
In natural conversation, Japanese often drops the subject or uses a name/title instead. You might hear simply: 昼寝をしないと具合が悪くなるみたい。

Can みたい attach to whole clauses like this without の?

Yes. みたいだ/ようだ can follow a full clause directly:

昼寝をしないと具合が悪くなるみたい(だ)。 When modifying a noun, use みたいな; when modifying a verb/adjective/adverbially, use みたいに.
子どもみたいな人 (a person like a child)
子どもみたいに笑う (laugh like a child)

Could I move みたい earlier in the sentence?

No. みたい modifies what immediately precedes it. Here it comments on the whole preceding clause. If you want to say “She seems to be the kind of person who…,” restructure:

彼女は、昼寝をしないと具合が悪くなる人みたいだ。

Is the comma after しないと required? I sometimes see one.

Punctuation is flexible in Japanese. A comma after the conditional can aid readability:

昼寝をしないと、具合が悪くなるみたい。 Both with and without the comma are fine.

Are spaces between the words normal in Japanese?

No. Standard Japanese writing does not insert spaces between words. They’re often added in teaching materials to help learners parse the sentence.

What are the readings of the key words, and is there any chance of confusing みたい with 見たい?

彼女（かのじょ）, 昼寝（ひるね）, 具合（ぐあい）, 悪く（わるく）.
みたい here is the conjectural “seems like.” 見たい（みたい） means “want to see.” They sound the same, so context (and kanji when written) disambiguates.

Can I use しなきゃ instead of しないと?

Yes, as a conditional it works (it’s a contraction of しなければ):

昼寝しなきゃ具合が悪くなるみたい。 Be aware that, like 〜ないと, standalone 〜なきゃ can also imply obligation when the result clause is omitted. Context tells them apart.