После вкусного завтрака я чувствовал прилив сил.

Because после requires the genitive case.

• после = after
• nouns after после go into the genitive
• any adjective describing that noun must also match the genitive

So:

• завтрак → nominative
• завтрака → genitive singular

And:

• вкусный → nominative masculine
• вкусного → genitive masculine singular

So после вкусного завтрака literally means after a tasty breakfast, with both words changed to genitive.

Because it is the genitive singular masculine form of the adjective вкусный.

Here is the pattern:

• nominative masculine: вкусный завтрак
• genitive masculine: вкусного завтрака

Since завтрак is a masculine singular noun, the adjective must agree with it in:

• gender
• number
• case

So after после, both words switch into the genitive:

• вкусный → вкусного
• завтрак → завтрака

Because чувствовал is past tense, while чувствую is present tense.

• я чувствую = I feel / I am feeling
• я чувствовал = I felt / I was feeling

Since the sentence describes a past situation, Russian uses the past tense form:

• чувствовать → чувствовал

Also, чувствовал shows that the speaker is male. A female speaker would say:

• я чувствовала

This is an aspect question.

• чувствовать is imperfective
• почувствовать is perfective

In this sentence, чувствовал presents the feeling as a state or ongoing experience:
I felt a surge of energy.

If you say почувствовал, it sounds more like the moment of noticing or beginning to feel it:

• После вкусного завтрака я почувствовал прилив сил.
  = After a tasty breakfast, I felt / noticed a surge of energy.

So both can work, but the nuance changes:

• чувствовал = the state/experience
• почувствовал = the moment it came on

Because прилив is the direct object of чувствовал.

The verb чувствовать usually takes a direct object in the accusative:

• чувствовать радость = to feel joy
• чувствовать усталость = to feel tiredness/fatigue
• чувствовать прилив сил = to feel a surge of energy

For masculine inanimate nouns, the accusative singular looks the same as the nominative singular.

So:

• nominative: прилив
• accusative: прилив

That is why the form does not visibly change.

Because Russian often uses the genitive after nouns like прилив to show what kind of surge/influx it is.

So:

• прилив = surge, influx
• сил = of strength / of energy

This is a very common pattern in Russian:

• чашка чая = a cup of tea
• кусок хлеба = a piece of bread
• прилив сил = a surge of energy

Here сил is the genitive plural of сила.

Even though сила means strength, Russian often uses the plural силы / сил in expressions about energy or strength.

Yes, it is a very common expression.

Прилив сил means:

• a surge of strength
• a burst of energy
• renewed energy

It sounds natural and idiomatic in Russian. Learners should treat it as a useful chunk of language.

Similar expressions include:

• почувствовать прилив сил = to feel a burst of energy
• ощутить прилив сил = to sense a surge of energy

So it is not just random vocabulary; it is a standard collocation.

Yes. Russian word order is fairly flexible.

This sentence starts with:

• После вкусного завтрака = After a tasty breakfast

This puts the time/context first.

You could also say:

• Я чувствовал прилив сил после вкусного завтрака.

That is also grammatical and natural.

The difference is mainly in focus and style:

• После вкусного завтрака я чувствовал прилив сил.
  Emphasizes the setting first: After breakfast...
• Я чувствовал прилив сил после вкусного завтрака.
  Starts with I felt..., so the experience itself comes first.

Because Russian has no articles.

English uses:

• a
• the

Russian does not have direct equivalents of these in normal grammar.

So вкусного завтрака can mean:

• a tasty breakfast
• the tasty breakfast

The exact interpretation depends on context.

That is completely normal in Russian.

Not here.

Russian has two common patterns:

• чувствовать что-то = to feel something
• чувствовать себя как-то = to feel a certain way

In this sentence, the object is прилив сил, so себя is not needed:

• я чувствовал прилив сил = I felt a surge of energy

But if you want to describe your condition with an adjective or adverb, you often use себя:

• Я чувствовал себя хорошо. = I felt good.
• Я чувствовал себя бодрым. = I felt energetic.

So:

• чувствовать прилив сил = feel a surge of energy
• чувствовать себя бодрым = feel energetic

Я is the subject: I.

Russian often can omit subject pronouns when the meaning is clear from context, but in the past tense this is less automatic than in the present, because past-tense verb forms show gender but not person as clearly.

So:

• Я чувствовал = clearly I felt
• Чувствовал прилив сил could mean I felt, but only if the context already makes the subject obvious

Including я makes the sentence clear and natural.

Yes, it can be tricky for learners.

A rough pronunciation is:

• CHOOS-tvo-val

A few useful points:

• the ч sounds like ch
• у sounds like oo
• the cluster вств is hard, and in fast speech some sounds may be reduced a bit
• the stress is on чу́вствовал

So the stressed part is the first syllable:

• чу́вствовал

It is a good word to practice slowly at first.