मुझे आज सिरदर्द है।

Because Hindi often expresses physical feelings, sensations, and conditions with a dative-style subject.

So instead of saying something like I am headache, Hindi says something closer to:

• मुझे ... है = to me ... is

In this sentence:

• मुझे = to me / for me
• सिरदर्द है = there is a headache

So मुझे आज सिरदर्द है literally feels like To me, today, there is a headache, which naturally means I have a headache today.

This pattern is very common in Hindi:

• मुझे भूख है = I am hungry / I have hunger
• मुझे प्यास है = I am thirsty
• मुझे ठंड लग रही है = I feel cold

मुझे is the oblique/dative form of मैं.

In simple learner-friendly terms, it often means:

• to me
• for me
• sometimes just me, depending on context

In this sentence, it marks the experiencer — the person who is having the condition.

So:

• मैं = I
• मुझे = to me / me

That is why मुझे आज सिरदर्द है is natural, but मैं आज सिरदर्द है is not grammatical.

Because the sentence is not structured as I am X.

If it were using मैं, then you might expect हूँ:

• मैं खुश हूँ = I am happy

But here, the structure is different:

• मुझे सिरदर्द है

The thing that grammatically exists is सिरदर्द (headache), which is treated as singular, so Hindi uses है.

A useful way to think of it:

• मैं खुश हूँ = I am happy
• मुझे दर्द है = I have pain / There is pain for me

So है matches the condition being stated, not मैं.

सिरदर्द is a compound noun:

• सिर = head
• दर्द = pain

So literally it means head-pain, i.e. headache.

You may also sometimes see it written as:

• सिर दर्द

But सिरदर्द as one word is very common and natural.

Yes, it is natural and standard.

It is a very common Hindi way to express a temporary physical problem or sensation.

Other natural variants include:

• आज मुझे सिरदर्द है।
• मुझे सिरदर्द है। = I have a headache.
• मेरा सिर दुख रहा है। = My head is hurting.

These are similar, but not exactly identical in tone:

• मुझे सिरदर्द है = I have a headache
• मेरा सिर दुख रहा है = My head hurts / is hurting

Both are useful and common.

Yes. Hindi word order is flexible, especially with time words like आज.

All of these are natural:

• मुझे आज सिरदर्द है।
• आज मुझे सिरदर्द है।
• मुझे सिरदर्द है आज। — possible, but often more conversational or emphatic

The most neutral versions are usually:

• मुझे आज सिरदर्द है
• आज मुझे सिरदर्द है

Placing आज first can slightly emphasize today.

Hindi usually does not use articles like a, an, and the the way English does.

So where English says:

• I have a headache

Hindi simply says:

• मुझे सिरदर्द है

The idea of a headache is understood from context. Hindi normally does not need a separate word for a here.

Not normally, if you mean I have a headache.

मेरा means my, so मेरा सिरदर्द would sound like my headache, as a noun phrase, not a complete natural way to express the condition.

For example:

• मुझे सिरदर्द है। = I have a headache.
• मेरा सिर दुख रहा है। = My head is hurting.

So if you want the standard expression for the condition, use:

• मुझे सिरदर्द है

They are close in meaning, but not identical.

1. मुझे सिरदर्द है

This means:

• I have a headache

It names the condition directly.

2. मेरा सिर दुख रहा है

This means:

• My head is hurting
• My head aches

This focuses more on the head hurting as an action/state in progress.

So:

• मुझे सिरदर्द है = the condition is a headache
• मेरा सिर दुख रहा है = the head is hurting

In everyday speech, both are common.

You add नहीं before है:

• मुझे आज सिरदर्द नहीं है।
• आज मुझे सिरदर्द नहीं है।

This means:

• I do not have a headache today.

That same pattern works with many similar sentences:

• मुझे भूख नहीं है। = I am not hungry.
• मुझे बुखार नहीं है। = I do not have a fever.

A simple yes/no question can be made by adding क्या at the beginning:

• क्या मुझे आज सिरदर्द है?

That literally means:

• Do I have a headache today?

But in real life, that exact question is a bit unusual unless someone is confused, joking, or asking about symptoms.

More natural questions would be:

• क्या तुम्हें आज सिरदर्द है? = Do you have a headache today?
• क्या आपको सिरदर्द है? = Do you have a headache? (polite)

So the grammar is correct, but the context matters.

A helpful rough pronunciation is:

• mujhe aaj sirdard hai

More roughly for an English speaker:

• moo-jhay aaj sir-dard hai

A few notes:

• मुझे sounds like mujhe; the झ sound is like a breathy j/h combination
• आज = aaj, with a long aa
• सिर = sir (not like English sir exactly, but close enough to start)
• दर्द = dard
• है is often pronounced close to hai

दर्द is generally treated as masculine, and सिरदर्द is also treated as masculine.

In this sentence, that matters because it takes:

• है for singular

Examples:

• मुझे सिरदर्द है। = I have a headache.
• मुझे बहुत तेज़ सिरदर्द है। = I have a very bad headache.

You do not see much visible gender agreement here beyond the normal singular form, but it is useful to know the noun is masculine.

Yes, very often.

This is one of the most useful Hindi patterns to learn:

• मुझे बुखार है। = I have a fever.
• मुझे खाँसी है। = I have a cough.
• मुझे दर्द है। = I am in pain / I have pain.
• मुझे नींद आ रही है। = I am feeling sleepy.
• मुझे भूख है। = I am hungry.

So मुझे ... है is a very important structure for expressing what someone is experiencing.