После разговора с начальницей мне было не до сна.

Because после always requires the genitive case in Russian.

• разговор = nominative
• разговора = genitive

So:

• после разговора = after the conversation / after talking

This is a fixed grammar rule:

• после урока = after the lesson
• после работы = after work
• после встречи = after the meeting

Начальницей is in the instrumental case because the preposition с here means with.

• начальница = a female boss / female superior
• с начальницей = with the female boss

Compare:

• с другом = with a friend
• с сестрой = with a sister
• с учительницей = with the female teacher

So разговор с начальницей means a conversation with the female boss.

Yes. Начальница is specifically feminine.

• начальник = male boss, or sometimes boss in a general masculine form
• начальница = female boss

So:

• с начальником = with a male boss
• с начальницей = with a female boss

This is an impersonal construction in Russian.

The phrase мне было не до сна literally works more like:

• to me it was not up to sleep
• more naturally: I was in no mood for sleep
• or: sleep was the last thing on my mind

Russian often uses the dative case for a person experiencing a state:

• мне холодно = I am cold
• мне грустно = I feel sad
• мне было не до шуток = I wasn’t in the mood for jokes

So мне means to me, and the whole structure expresses your state rather than describing you with я был.

Было is the neuter past tense form of быть.

In impersonal sentences like this, Russian often uses neuter singular past tense by default:

• мне было холодно
• нам было весело
• ему было трудно

There is no real subject like he/she/it here, so Russian uses было as the standard impersonal past form.

Не до + genitive is a common Russian expression meaning:

• not in the mood for
• not up to
• not the time for
• the last thing on one’s mind is...

So:

• не до сна = not up for sleep / not in the mood for sleeping / sleep was the last thing on my mind

It often suggests that someone is too upset, busy, stressed, shocked, or preoccupied for something.

Examples:

• мне сейчас не до шуток = I’m not in the mood for jokes right now
• ему было не до еды = he wasn’t thinking about food / he had no appetite
• нам не до отдыха = we’re not in a position to relax

Because the pattern не до + genitive requires the genitive case.

• сон = sleep (nominative)
• сна = genitive

So:

• не до сна
• не до работы
• не до смеха
• не до шуток

This is a fixed grammatical pattern.

Yes. In this sentence, разговор can be understood as:

• the conversation
• the talk
• talking

So после разговора с начальницей could be translated naturally as:

• After my conversation with my boss
• After talking with my boss
• After speaking with my boss

The exact English wording depends on style, but the Russian is very natural.

Russian often leaves out possessives like my, your, his, etc. when the meaning is clear from context.

So с начальницей can easily mean:

• with the boss
• with my boss

In many situations, English prefers my boss, but Russian does not always need моей начальницей.

If you wanted to make it explicit, you could say:

• После разговора с моей начальницей...

But in many cases that sounds unnecessary unless you want emphasis or clarity.

It sets the time/background for the main statement.

It means:

• after the conversation with the boss
• after talking with the boss

So the structure is:

• После разговора с начальницей = after speaking with the boss
• мне было не до сна = I was in no mood for sleep

Russian often puts this kind of time phrase at the beginning of the sentence, but it could be moved:

• Мне было не до сна после разговора с начальницей.

That is also grammatical, though the original word order sounds very natural.

Yes, usually.

• я не хотел спать = I didn’t want to sleep
• мне было не до сна = I was in no state for sleep / sleep was the last thing on my mind

The second one suggests a stronger emotional or mental reason: stress, worry, shock, agitation, and so on.

So after a serious talk with a boss, мне было не до сна sounds much more expressive than simply я не хотел спать.

Very likely, yes.

By itself, мне было не до сна suggests the speaker was too disturbed or preoccupied to sleep. So the conversation with the boss was probably:

• stressful
• upsetting
• serious
• emotionally intense

The sentence does not state this directly, but that is the natural implication.

Absolutely. Не до + genitive is very productive.

Examples:

• мне не до смеха = I’m not in the mood for laughing
• ему не до разговоров = he’s not up for talking
• нам не до праздника = we’re in no mood for a celebration
• ей было не до учёбы = studying was the last thing on her mind

So once you learn the pattern, you can use it in many situations.