Learn Hardcore Japanese: sensyuu kara karada ga omokute, kinou ha hirune sika dekinakatta. - Since last week my body has felt heavy, and yesterday I could do nothing but nap.

With time expressions, から marks the starting point: “since/from [that time].”
Without an end point stated, it implies the state continues up to the reference time (here, at least up to yesterday).
To stress continuity, add ずっと: 先週からずっと体が重い.
A more formal/ written alternative is 先週以来 (“since last week”): 先週以来、体が重い.

Why is it 重くて and not just 重い? What does the て-form do here?

重い is an -i adjective. Its て-form is 重くて (drop い, add くて).
The て-form links clauses. Here it means “(my body) is heavy, so…” or “and because…”, giving a reason for the next clause.
Alternatives for explicit causation:
- 先週から体が重かったので、昨日は… (polite/neutral, “since my body was heavy, …”)
- 先週から体が重いから、昨日は… (more casual).

Why is it 体が and not 体は?

For personal states/feelings with adjectives, Japanese often uses the pattern “X が Adjective”: 体が重い, 頭が痛い, 目がかゆい.
が marks the thing experiencing the state; the overall topic (“I”, “yesterday”, etc.) is handled elsewhere or omitted.
体は重い is possible but contrastive (“as for my body, it’s heavy (though something else isn’t)”).

Does 体が重い literally mean “the body is heavy”?

Literally yes, but idiomatically it means “I feel sluggish/heavy/tired,” not that you gained physical weight.
Near-synonyms: だるい, 重だるい, 体がだるい.
To talk about actual weight, you’d say 体重が増えた (“my weight increased”).

Why does 昨日 take は (as in 昨日は)? Could I drop it?

は topicalizes “yesterday”: “As for yesterday, …” It sets the timeframe and often implies contrast with other days.
You can drop は and just say 昨日、昼寝しかできなかった. That feels more like a simple time adverb.
Using は makes the contrast (“yesterday (unlike other days)”), or focus on that day, clearer.

How does しか work here? Do I always need a negative with it?

しか attaches to a noun/quantity and, together with a negative predicate, means “nothing but/only.”
The predicate must be negative: 昼寝しかできなかった = “I could do nothing but nap.”
Think of it as “except for N, not [do/be] anything.”
More examples:
- 水しか飲まない = “I drink only water.”
- 千円しか持っていない = “I have only 1000 yen.”

What’s the difference between しか and だけ?

しか + negative emphasizes limitation/insufficiency: “nothing but.” It often implies you couldn’t manage anything else.
- 昼寝しかできなかった = “I could do nothing but nap” (inability to do other things).
だけ is neutral “only” and does not require a negative.
- 昼寝だけした = “I only took a nap” (choice/fact, not inability).
Be careful: XだけVない means “X alone does not V,” which flips the meaning:
- 昼寝だけできなかった = “Napping was the only thing I couldn’t do.”
Avoid redundant だけしか together: 昼寝だけしかできなかった is considered incorrect/unnatural.

Can I move しか or 昨日は around? What word orders are natural?

Default and most natural: 昨日は昼寝しかできなかった.
You can place the time early: 昨日は、先週から体が重くて、昼寝しかできなかった.
昼寝しか昨日はできなかった is grammatical but marked; keep the しか-phrase right before the verb for the smoothest flow.
The しか-marked item stays adjacent to the verb phrase it limits.

Why is it できなかった and not しなかった?

できない expresses inability/capability: “cannot/could not.”
With しか, Xしかできない means “the only thing I can do is X.”
昼寝しかできなかった highlights limitation (“I couldn’t do anything except nap”).
昼寝だけした would describe what you did by choice; 昼寝をしなかった means “I didn’t nap,” which is the opposite of this sentence.

How does できる work with する-nouns like 昼寝? Which particle goes with it?

Activities like 昼寝 pair with する (“to nap”) or with できる for ability:
- Action: 昼寝をする (“to take a nap”).
- Ability: 昼寝ができる (“to be able to take a nap”).
In the potential/ability construction, the activity typically takes が, not を. Saying 昼寝をできる is generally avoided.
With しか, the underlying が is omitted: 昼寝しかできない.

How is tense being handled across the two parts?

The first clause uses the て-form (重くて) with the time frame 先週から, establishing an ongoing state that started last week.
The second clause is past negative (できなかった), specifying what happened yesterday.
Together: “Since last week, I’ve been feeling heavy, and (as a result) yesterday I could do nothing but nap.”

How would I say this more politely or formally?

Is 先週から体が重くなった okay? How does it differ from 先週から体が重い?

先週から体が重い: a state that has held since last week (“has felt heavy since last week”).
先週から体が重くなった: a change that started last week (“it became heavy starting last week”).
Use the first for an ongoing condition; use the second to highlight the onset/change.

Can I also use から as “because,” e.g., 先週から体が重いから、昨日は… even though there’s already a から?

Yes. The first から is “since (time),” and the second から is “because.” Japanese allows this; context disambiguates them:
- 先週から体が重いから、昨日は昼寝しかできなかった。

Could I use 以外 instead of しか to say “other than a nap, I couldn’t do anything”?

Yes: 昼寝以外はできなかった = “(I) couldn’t do anything except a nap.”
Include は (or には) after 以外 to mark the contrast. Without it (昼寝以外できなかった), it sounds off.

Who is the subject here? Why is “I” not stated?

Japanese often omits the subject when it’s obvious from context.
With personal physical states (体が重い, 頭が痛い), the speaker is normally understood to be the subject, so 私 is left out.
You could say 私は for contrast/emphasis, but it’s unnecessary here.