Learn Hardcore Malay: Jika saya minum susu panas sebelum tidur, kepala saya rasa lebih tenang. - If I drink hot milk before sleeping, my head feels calmer.

Jika sounds a bit more formal or “bookish”, and is common in writing, news, instructions, or essays.
Kalau is more colloquial and very common in speech. For a neutral, slightly formal sentence (like in a textbook), jika is a good choice.

Why is the second part “kepala saya rasa lebih tenang” and not something like “saya rasa kepala saya lebih tenang”?

In kepala saya rasa lebih tenang, the subject is kepala saya (my head), and rasa is the verb (feels), so the structure is:

kepala saya (subject) + rasa (verb) + lebih tenang (complement)

You can also say Saya rasa kepala saya lebih tenang (I feel my head is calmer), which is also natural.
The given sentence focuses directly on the head as the thing that feels calmer, while saya rasa… focuses on my feeling or perception. Both are grammatical; the nuance is just slightly different.

Why is there no explicit word meaning “will” or “would” in the Malay sentence?

Malay usually does not mark tense with separate words like will or would.
The sentence Jika saya minum susu panas sebelum tidur, kepala saya rasa lebih tenang can correspond to English:

“If I drink hot milk before sleeping, my head feels / will feel calmer.”

The time relationship (present, future, habitual) is understood from context. You only add time words like akan (will) if you really need to emphasize the future:
Jika saya minum susu panas sebelum tidur, kepala saya akan rasa lebih tenang.

Why is it susu panas and not panas susu?

In Malay, adjectives normally come after the noun they describe:

susu panas = hot milk (susu = milk, panas = hot)
kepala besar = big head
rumah baru = new house

So panas susu would sound wrong, because it is reversing the normal noun–adjective order.
Think of it as “milk (that is) hot”, “head (that is) big”, “house (that is) new”.

Do we need yang in susu panas? For example, should it be susu yang panas?

You don’t need yang here; susu panas is perfectly natural.
You add yang when you want to specifically highlight or define the adjective or clause, for example:

Saya mahu susu yang panas. = I want the milk that is hot (not cold one).
Susu panas on its own is more like “hot milk” as a general description.

In your sentence, we’re just describing the type of drink (hot milk), so susu panas is the normal form.

What exactly does sebelum tidur mean, and why isn’t it sebelum saya tidur?

Sebelum tidur literally means “before sleep / before sleeping”.
Malay often uses a bare verb like tidur (sleep) after time words like sebelum (before), selepas / sesudah (after), without saying I/you:

Sebelum makan, basuh tangan. = Before eating, wash (your) hands.
Selepas mandi, saya terus tidur. = After bathing, I went straight to sleep.

You could say sebelum saya tidur (before I sleep), and it’s also correct, but it’s longer and not necessary when it’s obvious who is sleeping.

What is the function of lebih in lebih tenang, and how do you form comparatives in Malay?

Lebih means “more”, so lebih tenang = “calmer / more calm”.
In Malay, comparatives are usually formed by putting lebih before an adjective:

lebih besar = bigger / larger
lebih cepat = faster / more quickly
lebih tenang = calmer / more calm

If you want to say “than X”, you add daripada:

kepala saya rasa lebih tenang daripada biasa
= my head feels calmer than usual.

What’s the difference between rasa, berasa, and merasa?

All three come from the root rasa (feel / taste / sense), but usage differs:

rasa (as a verb) in conversation:
kepala saya rasa lebih tenang = my head feels calmer.
Very common and natural in speech.
berasa is slightly more formal/literary:
kepala saya berasa lebih tenang – correct, but feels a bit more formal or old-fashioned in many contexts.
merasa usually means to taste (food) or to experience something:
Saya mahu merasa sup ini. = I want to taste this soup.
Saya mahu merasa hidup di luar negara. = I want to experience living abroad.

In your sentence, rasa (without prefix) is the most natural choice.

Why is it kepala saya (“my head”) and not saya directly (like “I feel calmer”)?

Using kepala saya focuses on the physical or mental state of the head (e.g. less heavy, less stressed).
It’s like saying “my head feels calmer / more relaxed”, which is common when talking about headaches, stress, or mental calmness.

You can say:

Saya rasa lebih tenang. = I feel calmer.
Saya rasa kepala saya lebih tenang. = I feel my head is calmer.

The original sentence just chooses to highlight the head as the part that benefits from the hot milk.

Is the word order in kepala saya rasa lebih tenang fixed, or can it be rearranged?

The natural basic order is:

kepala saya (subject) + rasa (verb) + lebih tenang (complement).

You cannot freely move words around like in some poetic English.
Forms like “kepala saya lebih tenang rasa” would sound wrong in normal Malay.

Some acceptable alternatives are:

Kepala saya berasa lebih tenang. (with berasa)
Saya rasa kepala saya lebih tenang. (different structure)

But you keep to the usual Subject–Verb–Object/Complement order.

Could I replace jika with bila here? How are jika, kalau, and bila different?

You could hear people say:

Bila saya minum susu panas sebelum tidur, kepala saya rasa lebih tenang.

In conversation, bila is often used like “when/if”.
However:

jika = if (more formal/written)
kalau = if (very common in speech)
bila = when; in spoken Malay it often overlaps with kalau, but in careful writing it’s more “when” than “if”.

For learners, it’s safest to use jika or kalau for “if”, and bila mainly for “when” unless you’re imitating casual speech.

Is susu singular or plural? Do I need to say “a glass of milk” in Malay?

Susu is a mass noun in Malay, like “milk” in English. It doesn’t have a plural form; context tells you how much.
If you need to be specific, you use classifiers:

segelas susu = a glass of milk
secawan susu = a cup of milk
sebotol susu = a bottle of milk

In your sentence, susu panas is general: hot milk (without specifying the quantity).

Is this sentence formal or informal? Is saya the polite form of “I”?

Yes, saya is the polite / neutral pronoun for “I”.
The whole sentence is in a neutral to slightly formal style (mainly because of jika and saya).

In more casual speech with friends, some speakers might say:

Kalau aku minum susu panas sebelum tidur, kepala aku rasa lebih tenang.

Here aku is an informal “I”, and kepala aku matches it.
For speaking with strangers, elders, or in class, saya is the safest choice.

Could the sentence be simplified to Jika saya minum susu panas sebelum tidur, saya rasa lebih tenang? Would that change the meaning?

Yes, that’s a perfectly natural alternative:

Jika saya minum susu panas sebelum tidur, saya rasa lebih tenang.
= If I drink hot milk before sleeping, I feel calmer.

Now the focus is on you as a whole person feeling calmer, not specifically your head.
The overall idea (hot milk before bed leads to a calmer state) is the same; it’s just a slightly different emphasis.