Ночью мне иногда не спится, потому что я думаю о своём проекте.

Ночью is the instrumental form of ночь, used adverbially to mean “at night / during the night.”

Russian often uses the instrumental case as an adverbial form for time:

• днём – in the daytime
• утром – in the morning
• вечером – in the evening
• ночью – at night

You could say ночью мне не спится or мне не спится ночью; both are fine.
В ночь is rare and has a more literary or specific meaning (“into the night,” often describing movement into the night).

Literally, мне не спится is something like “it doesn’t sleep to me” – this is an impersonal construction. There is no grammatical subject like “I” or “it”; the verb is in 3rd person singular (спится) and the experiencer is in the dative (мне).

Nuance:

• я не сплю – “I am not sleeping.”
  Neutral statement of fact: I’m awake (this could be by choice or circumstance).

• мне не спится – “I can’t sleep / I don’t feel like sleeping / sleep won’t come.”
  Emphasizes a state where sleep just doesn’t happen, often involuntarily, sometimes with emotion or discomfort implied.

In the sentence, мне иногда не спится is more natural than я иногда не сплю, because the focus is on the difficulty or inability to fall asleep.

Спится is the 3rd person singular, present tense of спаться, which is спать + -ся.

• спать – to sleep
• спаться – literally “to sleep (for someone),” used impersonally to talk about how someone is able to sleep.

Typical patterns:

• Мне хорошо спится. – I sleep well / I can sleep well.
• Ему плохо спится. – He sleeps badly.
• Ночью мне не спится. – At night I can’t sleep.

So it’s not a completely different verb with a new meaning; it’s derived from спать and specialized for these impersonal, “it sleeps to me” type constructions.

In Russian impersonal constructions, the person who experiences the state is often in the dative case. There is no grammatical subject; the verb is usually 3rd person singular or neuter.

Examples:

• Мне холодно. – I am cold.
• Тебе трудно. – It’s hard for you.
• Ему не спится. – He can’t sleep.

So in мне не спится, мне is dative: the one who is affected by the situation of “not sleeping.” Using я would force a different, personal structure: я не сплю.

Иногда is an adverb meaning “sometimes”.

In this sentence, it modifies the whole situation “не спится”:

• Ночью мне иногда не спится… – Sometimes at night I can’t sleep…

Common positions:

• Ночью мне иногда не спится.
• Иногда ночью мне не спится.
• Ночью иногда мне не спится.

All are grammatical; Russian is quite flexible with adverb placement. The differences are mainly in rhythm and emphasis, not in core meaning. The original order is very natural and neutral.

Yes, you can say:

• Мне иногда не спится ночью, потому что…

This is also correct and very natural.

Difference:

• Ночью мне иногда не спится… – slight emphasis on “at night” (as the time when this happens).
• Мне иногда не спится ночью… – slight emphasis on “me / sometimes I” and then you clarify “at night.”

Semantically they both mean “Sometimes at night I can’t sleep…”; it’s mostly word-order nuance.

The general rule in Russian is that не goes directly before the word it negates, usually the verb:

• не спится – does not sleep / can’t sleep
• не думаю – do not think
• не читаю – do not read

Here, the negation is of the state of sleeping, so не comes before спится:

• мне не спится

You might see иногда or other adverbs between the dative and the verb, but не normally sticks to the verb it negates:

• мне иногда не спится – natural
• мне не иногда спится – very strange; would suggest you’re negating “sometimes”, which doesn’t fit.

The imperfective aspect думаю describes an ongoing, repeated, or processual action:

• я думаю о своём проекте – I think / I am thinking about my project (process, often lasting some time).

The perfective подумать would describe a completed, one-time act of thinking:

• я подумаю – I will think (about it, once, to make a decision).

In the sentence, the cause of not sleeping is a continuous mental process at night, not a single completed act. That’s why the imperfective я думаю is used.

You can say both:

• …потому что я думаю о своём проекте.
• …потому что думаю о своём проекте.

Russian often omits personal pronouns (я, ты, он, etc.) because the verb ending already shows the person.

Including я:

• Can add a bit more clarity or emphasis on “I,” especially in more formal or careful speech.

Omitting я:

• Sounds a bit more informal, conversational, and is very common.

Meaning is effectively the same; it’s a stylistic choice.

Both can be correct, but there is a nuance:

• свой is the reflexive possessive (“one’s own”).
  It’s used when the possessor is the same as the subject of the clause.

Here, the subject of думаю is я, so свой refers back to я:

• я думаю о своём проекте – I am thinking about my (own) project.

If you said:

• я думаю о моём проекте, it’s still understandable, but sounds a bit heavier / more marked, and sometimes can hint at contrast (“about my project (not someone else’s)”).

Natural Russian strongly prefers свой in such cases, unless there is a reason to stress мой.

Своём проекте is in the prepositional case singular after the preposition о:

• о ком? о чём? – about whom? about what?

Declension:

• свой (masc./neut. sg. prepositional) → своём
• проект (masc. sg. prepositional) → проекте

So:

• о своём проекте – about my (own) project.

The ending -ем in своём and -е in проекте are regular prepositional singular endings.

Both о and про can mean “about,” but they differ in style:

• о (об)

  • prepositional – neutral / standard
  • думаю о своём проекте – I think about my project.

• про

  • accusative – more colloquial / informal, more like “about” in conversation, stories, movies, etc.
  • говорить про проект – to talk about the project.

With думать, о + prepositional (думать о чём-то) is the standard choice, especially in neutral or slightly formal language.
Думать про exists but is more colloquial and sounds less careful.

Потому что is a causal conjunction meaning “because”. It introduces the reason:

• …мне иногда не спится, потому что я думаю о своём проекте.
  – I sometimes can’t sleep at night because I’m thinking about my project.

Possible alternatives:

• так как – also “because,” a bit more formal or bookish:

  • …мне иногда не спится, так как я думаю о своём проекте.

• из-за того что – “because / due to the fact that,” often with a slightly more negative / burdensome nuance:

  • …мне не спится из-за того, что я думаю о своём проекте.

Потому что is the most neutral and common choice in everyday speech here.

Yes. In Russian, потому что almost always introduces a subordinate clause of reason, and a comma is required before it:

• Главная часть, потому что придаточная часть.

So:

• Ночью мне иногда не спится, потому что я думаю о своём проекте.

Leaving out the comma would be considered a punctuation error in standard written Russian.