Learn Hardcore Russian: После кофе мне не спится, и сон не приходит. - After coffee I can’t sleep, and sleep doesn’t come.

После requires the genitive case: после чего?
The word кофе is an indeclinable noun for most speakers, so it usually looks the same in every case. Here it is still genitive in meaning, even though the form doesn’t change: после кофе = after coffee.

Why is it мне and not я? What case is мне?

Мне is dative case (from я → мне).
With certain “state” constructions in Russian, the person experiencing the state is often in the dative:

мне холодно (I’m cold)
мне грустно (I’m sad)
мне не спится (I can’t sleep / I’m not sleepy / sleep won’t come)

So мне marks the experiencer, not the grammatical subject.

What does (не) спится mean literally, and why is it not just сплю?

Спится is an impersonal form built from спать. It expresses how sleep is “going” for someone (often like “it sleeps” in a very loose literal sense).

Я не сплю = I am not sleeping (a factual statement: I’m awake).
Мне не спится = I can’t sleep / I’m unable to fall asleep / sleep isn’t happening for me (more about the inability or the state, not just the fact).

It’s very common in Russian to use this impersonal style for involuntary states.

Why does спится have -ся? Is it reflexive?

The -ся here is part of an impersonal/reflexive-style verb form, but it’s not “reflexive” in the sense of doing something to yourself.
Many Russian verbs with -ся can form impersonal expressions about states or ease/difficulty:

мне легко работается (it’s easy for me to work / work goes easily)
мне плохо дышится (it’s hard for me to breathe)
мне не спится (I can’t sleep)

So -ся helps create that “it goes / it happens” feeling.

Is После кофе мне не спится the same as От кофе мне не спится?

They’re close, but not identical.

После кофе focuses on timing: after I drink coffee, I can’t sleep.
От кофе emphasizes cause: because of coffee (coffee is the reason), I can’t sleep.

In many contexts both work, but от sounds more explicitly causal.

Why is there a comma before и?

Because и is joining two independent clauses (each could stand as its own sentence):
1) После кофе мне не спится
2) сон не приходит

In Russian, a comma is typically required when и connects two full clauses.

What’s the difference between сон не приходит and я не засыпаю?

сон не приходит is more figurative/literary: sleep is not coming to me.
я не засыпаю is more direct and neutral: I’m not falling asleep.

Both are natural; the first sounds more expressive.

Why is it сон не приходит (present tense) if it’s about a general situation? Could it be past or future?

Russian present tense often describes a current repeated/general situation: “(right now / generally) sleep doesn’t come.”
You can change the tense depending on context:

Past: После кофе мне не спалось, и сон не приходил.
Future: После кофе мне не будет спаться, и сон не придёт. (or не будет приходить, depending on nuance)

The given sentence reads naturally as “this is what happens (now/usually).”

Why is сон the subject in the second clause, but there’s no subject in the first clause?

Because the first clause is impersonal: the verb form спится doesn’t take a normal subject (я/он/она) in this construction; instead it uses the dative experiencer (мне).
The second clause is a regular personal clause where сон is the grammatical subject: сон не приходит.

Could I say сон ко мне не приходит? What does that change?

Yes. Сон ко мне не приходит is possible and adds emphasis on “to me”: sleep isn’t coming to me (as opposed to others).
The original сон не приходит is more general and smoother; ко мне makes it a bit more explicit and emotional.

Is the word order fixed? Could I rearrange it?

Word order is flexible, but changes emphasis:

После кофе мне не спится (neutral)
Мне после кофе не спится (emphasizes “to me”)
Не спится мне после кофе (more expressive, literary)

Similarly:

и сон не приходит (neutral)
и не приходит сон (more poetic/emphatic)

All can be correct, but the original sounds very natural.

Why is не used twice? Is this a “double negative” like in English?

It’s not a double negative in the English sense. Each не negates its own verb:

не спится = cannot sleep
сон не приходит = sleep does not come

Russian commonly uses multiple negatives across clauses without “cancelling out.”