potatoさんの英文は惜しいです！
まず、雨の日はいつも眠くなると言っているので、Rainy day と単数ではなく Rainy days と複数にしてあげます。
主語が複数になったことで makes の ３人称単数の s はとってあげます。
あと「いつも」の always を足してあげると良いでしょう。
Rainy days always make me feel sleepy.
または
2) I always get sleepy on rainy days.
「私はいつも雨の日に眠くなる。」
get sleepy で「眠くなる」
on rainy days で「雨の日に」
ご参考になれば幸いです！
"I always feel sleepy on rainy days."
Always - something that repeatedly happens. "Tom is always late for the morning meeting,"
Sleepy - Tired and wanting to sleep. "The little boy looked sleepy on the train."
You could also say, "Rainy days make me feel tired."
Tired - Meaning to be in need of sleep.
"I always feel sleepy on rainy days."（雨の日はいつも眠くなる）
Always - 繰り返し起こる
例：
"Tom is always late for the morning meeting,"
（トムはいつも朝礼に遅れる）
Sleepy - 疲れて眠い
例：
"The little boy looked sleepy on the train."（その男の子は電車で眠そうにしていた）
次のように言うこともできます。
"Rainy days make me feel tired."（雨の日は眠くなる）
Tired - 眠い
Other ways to say this include:
"I always want to sleep in on rainy days." ("Sleep in" means to oversleep, usually on purpose.)
"I never want to get out of bed on rainy mornings."
"I always sleep better on rainy nights."
これは、次のように言うこともできます。
"I always want to sleep in on rainy days."（雨の日はなかなか起きられない）
※ "Sleep in" は「〔普通は意図的に〕遅くまで寝る」という意味です。
"I never want to get out of bed on rainy mornings."（雨の朝はなかなか起きられない）
"I always sleep better on rainy nights."（雨の夜はいつもよく眠れる）
Any of the following statements are appropriate:-
1. I always feel sleepy when it rains.
2. On rainy days l tend to get heavy-eyed.
Heavy-eyed is another expression for sleepy.Other words that mean the same thing as sleepy are drowsy, dozy, sluggish.
どちらの文も使うことができます。
1. I always feel sleepy when it rains.（雨が降るといつも眠くなる）
2. On rainy days I tend to get heavy-eyed.（雨の日は眠くなりやすい）
"Heavy-eyed" は "Sleepy"（眠い）の別の言い方です。他に、"Drowsy" "Dozy" "Sluggish" なども "Sleepy" の同義語です。
"The rain makes me feel sleepy."
'Sleepy' is an adjective which means tired. You can use the structure '(something/someone) makes me feel (adjective)' to express the fact that this person or thing contributes to your mood. For example, "sugar makes me feel energetic."
"I often feel lethargic on rainy days."
'Lethargic' also means sleepy or having little energy.
"The rain makes me feel sleepy."（雨の日は眠くなる）
'Sleepy' は「眠い」という意味の形容詞です。'(something/someone) makes me feel (adjective)' で「（もの／人）のせいで（形容詞）の気分になる」と言えます。
例：
"Sugar makes me feel energetic."（砂糖を食べると元気が沸いてくる）
"I often feel lethargic on rainy days."（雨の日はよく無気力になる）
'Lethargic' も「眠い／気力が沸かない」という意味です。
1.Rainy days always fill me with lethargy.
If something fills you with lethargy then it means
that you feel sapped or drained of energy and you find
it difficult to do absolutely anything that requires
physical or mental strength.
2. I cannot summon up any energy when it rains.
To summon up energy means finding the will or the
enthusiasm to complete a task. "I couldn't summon
up the energy to get out of bed so I called in sick."
1. Rainy days always fill me with lethargy.（雨の日は気力が沸かない）
"something fills me with lethargy" は「気力が沸かない／やる気が起きない」という意味です。
2. I cannot summon up any energy when it rains.（雨の日は気力が沸かない）
"To summon up energy" は「やる気を呼び起こす」という意味です。
"I couldn't summon up the energy to get out of bed so I called in sick."
（ベッドから出る気力がなかったので、病欠の電話を入れました）
"The rain causes me to feel like I have low energy which makes me sleepy"
If you wanted to explain that rainy days always make you feel sleepy, you could say any of the following statements: "Rainy days always make me feel sleepy", "The rain seems to make me feel very sleepy" or "The rain causes me to feel like I have low energy which makes me sleepy".
「雨の日はいつも眠くなる」は次のように言えます。
"Rainy days always make me feel sleepy"（雨の日はいつも眠くなる）
"The rain seems to make me feel very sleepy"（雨が降ると眠くなる気がする）
"The rain causes me to feel like I have low energy which makes me sleepy"（雨が降るとなんだか気が重くなる、眠くなってくる）
I always feel like falling asleep on rainy days like that.
I always feel so sleepy on rainy days.
I always get sleepy on rainy days.
potatoさん
ご質問どうもありがとうございます。
様々な表現があると思いますが、いくつか自然な表現を紹介します。
- I always feel like falling asleep on rainy days like that.
- I always feel so sleepy on rainy days.
- I always get sleepy on rainy days.
--- feel like doing XY = 「～したい気分」になる
お好みに合わせて使い分けてみてください。
ご参考にしていただければ幸いです。
I never have any energy, when it's raining outside. I just want to sleep.
When it's dismal with rain outside, I want to curl up and go to sleep.
The rainy days make me tired.
All of the above sentences can describe feeling sleepy on rainy days.
Dismal: means, Gloomy, bleak. When it's cloudy and raining and there is no blue sky, we can describe this as a dismal day. When it's dismal outside, I always want to sleep.
上のどの文を使っても「雨の日は眠くなる」と伝えることができます。
Dismal: 暗い／どんよりした。どんよりした雨の日は 'dismal day' と表すことができます。
When it's dismal outside, I always want to sleep.（どんよりした日は、眠くなる）
If you would like to explain that rainy days make you tired, you can say something like "I always get super sleepy on a rainy day." or "Rainy days make me super sleepy." These are both easy ways to explain this.
「雨の日は眠くなる」は次のように言えます。
"I always get super sleepy on a rainy day."（雨の日はすごく眠くなる）
"Rainy days make me super sleepy."（雨の日はすごく眠くなる）
どちらもシンプルな言い方です。
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