Learn Hardcore Russian: После такого спокойного вечера моё самочувствие утром лучше, чем после любого стрессового дня. - After such a calm evening my well-being in the morning is better than after any stressful day.

Adjectives and pronouns ending in -ой / -ый / -ий → -ого
- такой → такого
- спокойный → спокойного
Most masculine nouns ending in a consonant add -а or -я
- вечер → вечера

So:

такой спокойный вечер
becomes
такого спокойного вечера (after после)

Why is моё самочувствие neuter? Shouldn’t it be masculine or feminine?

In Russian, grammatical gender is mostly arbitrary and tied to word endings, not natural gender.

самочувствие ends in -ие, which is a typical neuter ending.
Therefore, its gender is neuter.
The possessive pronoun must agree with it in gender, number, and case, so we use the neuter nominative singular form моё.

Pattern:

Masculine: мой вечер
Feminine: моя книга
Neuter: моё самочувствие

So моё самочувствие is correct because самочувствие is neuter.

Why is моё самочувствие in the nominative case here?

Моё самочувствие is the subject of the sentence.

The basic structure is:

(После такого спокойного вечера) – adverbial phrase of time (after such a calm evening)
моё самочувствие – subject
утром – adverbial (when? in the morning)
лучше – predicate (is better)
чем после любого стрессового дня – comparison phrase

In Russian present tense, you generally omit the verb есть (to be), so:

Underlying structure is: моё самочувствие утром (есть) лучше.
The subject of (есть) лучше must be in the nominative, hence моё самочувствие.

Why is there no word for is in моё самочувствие утром лучше?

Russian usually omits the present tense of “to be” (есть) in simple sentences like this.

Full logical form: Моё самочувствие утром есть лучше…
Natural spoken/written Russian: Моё самочувствие утром лучше…

So when you see a Russian sentence like:

X лучше, чем Y

you should understand it as X is better than Y, even though is is not written or spoken.

What exactly is утром? Is it a noun or an adverb, and how is it different from утро?

Утром is historically the instrumental singular of the noun утро (morning), but in modern Russian it behaves like an adverb of time: in the morning.

Compare:

утро – morning (noun, nominative: the morning)
- Утро было холодным. – The morning was cold.
утром – in the morning (adverbial use)
- Я чувствую себя лучше утром. – I feel better in the morning.

Other common time adverbials formed similarly:

днём – in the daytime
вечером – in the evening
ночью – at night (this one is a slightly different pattern but same idea: adverbial time form)

So in the sentence, утром answers когда? (when?) → in the morning.

Can we move утром or the phrase после такого спокойного вечера to other positions? How flexible is the word order?

Yes, Russian word order is relatively flexible, especially with adverbials like time expressions. All of these are grammatically correct, with slight changes in emphasis:

После такого спокойного вечера моё самочувствие утром лучше, чем после любого стрессового дня.
– Neutral, starts by setting the context after such a calm evening.
Моё самочувствие утром после такого спокойного вечера лучше, чем после любого стрессового дня.
– Focuses more on my condition in the morning, then specifies after such a calm evening.
Утром моё самочувствие лучше после такого спокойного вечера, чем после любого стрессового дня.
– Emphasizes in the morning at the beginning.

Meaning stays the same; what changes is what feels most prominent in the sentence. The original order is very natural and clear.

What does самочувствие really mean here? Is it more like mood, health, or how I feel?

Самочувствие is best understood as how you feel physically and mentally, often with a health nuance.

It is broader than:

настроение – mood and a bit narrower/more subjective than:
здоровье – health

Examples:

У меня сегодня плохое самочувствие. – I’m not feeling well today.
Самочувствие пациента улучшилось. – The patient’s condition has improved.

In this sentence, it naturally means something like my overall condition / how I feel (physically and mentally).

How does the comparative лучше, чем… work here? Is чем always required with лучше?

Лучше is the comparative of хорошо or хороший (better).
The standard construction is:

X лучше, чем Y – X is better than Y

In your sentence:

моё самочувствие утром лучше, чем после любого стрессового дня

Literally:
my condition in the morning is better than (it is) after any stressful day

About чем:

It is the usual word for than in comparisons.
Sometimes in short, simple comparisons it can be omitted, especially in colloquial speech, but with a long phrase like после любого стрессового дня, keeping чем is more natural and clearer.

So here, чем is recommended and sounds completely standard.

Why is it после любого стрессового дня at the end, and why are those words also in the genitive?

The phrase после любого стрессового дня repeats the same structure as at the beginning:

Preposition после → requires genitive case.

Base forms:

любой стрессовый день – any stressful day (nominative)

Genitive singular:

любой → любого
стрессовый → стрессового
день → дня

So we get:

после любого стрессового дня

This phrase is part of the comparison:

лучше, чем после любого стрессового дня
– better than (it is) after any stressful day.

What is the nuance of любой in любого стрессового дня? How is it different from каждого or from just стрессового дня?

Любой roughly means any (at all), often with the sense it does not matter which one.

Nuances:

любой стрессовый день – any stressful day, no matter which; emphasizes generality and totality.
каждый стрессовый день – every stressful day, focuses more on each instance in a series.
Just после стрессового дня – after a stressful day (one such day, more generic, less strongly generalizing).

In this sentence, после любого стрессового дня suggests:

better than after any stressful day whatsoever,
not just a particular stressful day, but all stressful days in general.

Is стрессовый день the most natural way to say a stressful day, or would напряжённый день be better?

Both are possible, but they have slightly different flavors:

стрессовый день – a day that causes stress, a stressful day (direct link to stress as a psychological/physiological load).
напряжённый день – a tense / intense / hectic day: a lot of work, pressure, activity. It often implies stress, but focuses more on intensity and tension.

In everyday speech, for something like workdays or life in general, стрессовый день is normal and immediately understandable.
If you wanted to emphasize overwork, tight schedule, or constant rush, напряжённый день could sound even more natural.

Your original любого стрессового дня is perfectly good Russian for any stressful day in a health/feelings context.