Learn Hardcore Spanish (Latin America): Hablo conmigo mismo cuando estoy muy nervioso.

Hablo = I speak (first person singular)
So yo is not required. The sentence Yo hablo conmigo mismo… is grammatically correct, but it sounds more emphatic, like:
Yo hablo conmigo mismo… = I talk to myself (as opposed to someone else).

Most of the time, native speakers drop the subject pronoun unless they want to emphasize or clarify it.

What does conmigo mean, and why isn’t it con mí?

Conmigo literally comes from con + mí (with + me), but in modern Spanish it’s always written and pronounced as one special word: conmigo.

Spanish has three special forms with con:

conmigo = with me
contigo = with you (informal singular)
consigo = with him/her/oneself (more formal/literary or a bit old‑fashioned in everyday speech)

You should not say ✗ con mí or ✗ con ti; they sound incorrect. Always use conmigo / contigo / consigo.

What is the function of mismo in conmigo mismo?

Mismo adds the idea of “self” for emphasis:

conmigo = with me
conmigo mismo = with myself / with me myself

In English, “I talk to myself” uses myself to stress that you talk to you, not to another person.
In Spanish, mismo plays that emphatic role. It’s common in expressions like:

Yo mismo lo haré. – I’ll do it myself.
Se habla a sí mismo. – He talks to himself.

Is conmigo mismo necessary, or could I just say conmigo?

You can say only conmigo, but the meaning is slightly less explicit.

Hablo conmigo. – Literally I talk with me. Context would usually make people understand I talk to myself, but it sounds a bit unusual on its own.
Hablo conmigo mismo. – Clearly I talk to myself.

In practice, other very natural ways to say this are:

Hablo solo cuando estoy muy nervioso. – I talk to myself when I’m very nervous.
Me hablo a mí mismo cuando estoy muy nervioso. – I talk to myself when I’m very nervous.

All of these can be used, but hablar solo is extremely common in everyday speech.

If the speaker is a woman, does the sentence change?

Yes, the adjective and mismo must agree in gender with the speaker.

Man: Hablo conmigo mismo cuando estoy muy nervioso.
Woman: Hablo conmigo misma cuando estoy muy nerviosa.

Mismo/misma agrees with the person it refers to, and nervioso/nerviosa agrees with the subject (yo, even if it’s not written):

yo (man) → mismo, nervioso
yo (woman) → misma, nerviosa

Why is it estoy and not soy nervioso?

Spanish uses estar and ser differently:

estar nervioso = to be nervous right now / in this situation (temporary state)
ser nervioso = to be a nervous person by nature (a more permanent trait)

In cuando estoy muy nervioso, the idea is when I’m very nervous (in those moments), so estar is correct.

If you say Soy muy nervioso, you’re describing your personality: I’m a very nervous person (in general).

Why is it muy nervioso and not mucho nervioso?

Because muy and mucho are used with different types of words:

muy modifies adjectives and adverbs
- muy nervioso – very nervous
- muy rápido – very fast
mucho modifies nouns or can be an adverb with verbs
- mucho trabajo – a lot of work
- trabaja mucho – he works a lot

Since nervioso is an adjective, the correct intensifier is muy nervioso, not ✗ mucho nervioso.

Can I change the order and say: Cuando estoy muy nervioso, hablo conmigo mismo?

Yes. Both orders are correct and natural:

Hablo conmigo mismo cuando estoy muy nervioso.
Cuando estoy muy nervioso, hablo conmigo mismo.

In Spanish, you can freely place the cuando‑clause before or after the main clause. If it comes first, you usually write a comma after it, just like in English.

Why is the simple present (hablo / estoy) used, instead of something like “I am talking / I get nervous”?

The Spanish presente de indicativo is used for:

Habitual actions:
- Hablo conmigo mismo cuando estoy muy nervioso.
  = I talk to myself when I am very nervous (whenever that happens).
Current facts or states:
- Estoy muy nervioso. – I’m very nervous (right now).

To emphasize that something is happening right now as a continuous action, Spanish can use the progressive:

Estoy hablando conmigo mismo. – I am (right now) talking to myself.

But for general habits like in your sentence, the simple present is the normal choice.

Could I say Hablo solo cuando estoy muy nervioso instead? Does it mean the same?

Yes, that’s a very natural alternative, and in everyday Latin American Spanish it’s often even more common:

Hablo solo cuando estoy muy nervioso. – I talk to myself when I’m very nervous.

Notes:

solo here means “alone / by myself”, and in this context it’s understood as talking to oneself.
Don’t confuse it with sólo = only (this accent is now usually omitted in modern spelling, and context shows the meaning).

So:

Hablo solo ≈ I talk to myself / I talk when I’m alone.

Why is there no word for “to” in I talk to myself?

English needs “to” with the verb talk: talk to someone.
In Spanish, hablar can work differently:

With con (with):
- Hablo contigo. – I talk with you / I talk to you.
- Hablo conmigo mismo. – I talk with myself / I talk to myself.
With an indirect object (especially with a pronoun and a):
- Le hablo a mi hermano. – I talk to my brother.
- Me hablo a mí mismo. – I talk to myself.

So in Hablo conmigo mismo, the idea of “to” is built into the construction hablar con (“speak with”), so no separate word for “to” is needed.

Is conmigo mismo considered reflexive, even though there’s no me?

It’s reflexive in meaning, but not in the strict grammatical sense of using a reflexive verb with a pronoun like me, te, se attached to the verb.

Two ways to express “I talk to myself”:

Using hablar con
- conmigo mismo (prepositional phrase):
- Hablo conmigo mismo. – I talk to myself.
  Here, conmigo mismo expresses that the subject and the object are the same person.
Using a reflexive pronoun:
- Me hablo a mí mismo. – I talk to myself.
  Here me is a true reflexive pronoun attached to the verb hablo.

Both are correct and natural; the first is a bit simpler in form, the second is more clearly “reflexive” in grammar.