Learn Hardcore Russian: Психотерапевт сказал, что осознанное дыхание помогает расслабляться. - The psychotherapist said that mindful breathing helps to relax.

It is masculine singular past tense, so it tells you the psychotherapist is:
- one person, and
- grammatically masculine.
If the speaker were female, you would say сказала.
If it were plural:
- mixed group or all men: сказали
- group of women: also сказали (Russian past plural does not mark gender).

Сказать is perfective (focus on the completed act of saying, one event).
The imperfective partner is говорить (to speak, to be saying), e.g.:

Психотерапевт говорил, что… – The therapist was saying / used to say that…

In this context, сказал is natural because it refers to one statement made at some point.

Why is there a comma before что, and what does что do here?

Here что means that and introduces a subordinate clause (reported speech / a content clause):

Психотерапевт сказал, что … = The psychotherapist said that …

In Russian, a comma is always used before что when it introduces a subordinate clause like this. The pattern is very common:

Он думает, что… – He thinks that…
Я знаю, что… – I know that…

So the comma is required by standard punctuation rules.

What are the gender and case of психотерапевт, and why is it in that form?

Психотерапевт is a masculine noun in the nominative singular.

It is the subject of the main clause:
- Психотерапевт (subject) сказал (verb).

In Russian, the default word order is Subject–Verb–Object, and subjects are in the nominative case.

You could also say:

Сказал психотерапевт.

The meaning is the same (said the psychotherapist), but the emphasis shifts slightly to the verb first. The case (психотерапевт in nominative) does not change.

What is the grammatical role of осознанное дыхание, and why is it in that form?

Осознанное дыхание is a noun phrase:

дыхание – breathing, breath (neuter noun)
осознанное – mindful, conscious (adjective)

Дыхание is the subject of the subordinate clause:

…что осознанное дыхание помогает расслабляться.
- subject: осознанное дыхание
- verb: помогает
- infinitive: расслабляться

Because дыхание is neuter singular, nominative, the adjective must agree:

Neuter nominative singular ending -ое → осознанное дыхание.

So grammatically, осознанное дыхание is nominative neuter singular, functioning as the subject of помогает.

Why is помогает in third person singular, and what is its aspect and tense?

Помогает is:

present tense
third person singular
imperfective
from the verb помогать (to help).

It agrees with its subject:

subject: осознанное дыхание (it)
verb form: помогает (it helps).

So the structure is X помогает Y – X helps Y (with Y often expressed by an infinitive or a dative noun).

The imperfective aspect here expresses a general, repeated or typical effect:

Осознанное дыхание помогает расслабляться.
Mindful breathing (generally) helps (people) relax.

If you used perfective помочь (to help once), you’d get something like:

Осознанное дыхание может помочь расслабиться. – Mindful breathing can help (you) relax (on a specific occasion).

What does расслабляться mean exactly, and why does it end in -ться?

Расслабляться means to relax (intransitive, about yourself, to become relaxed).

The ending -ться (or -ся after vowels) marks a reflexive verb:

расслаблять – to relax (something/someone)
расслабляться – to relax (yourself), to become relaxed

Russian uses -ся / -сь both for:

truly reflexive actions (wash yourself, dress yourself, etc.)
intransitive or “middle voice” meanings (the door opens, the process continues).

Here it’s essentially to relax (oneself). That is why with помогать you get:

помогает расслабляться – helps (someone) relax.

What is the difference between расслабляться and расслабиться, and why is расслабляться used here?

They are an aspect pair:

расслабляться – imperfective, to be relaxing / to relax in general, as a process or repeated action
расслабиться – perfective, to relax (reach a relaxed state, one-time result)

In this sentence, расслабляться is used because the statement is about a general ability or tendency:

mindful breathing helps with the process of relaxing
it is about relaxation in general, not about one specific moment of becoming relaxed.

If you said:

Осознанное дыхание помогает расслабиться.

this would sound more like it helps (you) manage to relax (reach the relaxed state), a bit more result-oriented. Both are possible, but расслабляться focuses more on the ongoing process / practice of relaxing.

Could we use a noun instead of the infinitive, like помогает с расслаблением?

Native Russian strongly prefers помогать + infinitive in this type of sentence:

помогает расслабляться – helps (to) relax.

While помогает с расслаблением is grammatically possible, it sounds heavy and unnatural in everyday speech and less idiomatic. The default pattern is:

помогать + infinitive
помогает засыпать – helps (you) fall asleep
помогает учиться – helps (you) study

So помогает расслабляться is the natural choice.

Is осознанное дыхание a fixed phrase in Russian, like mindful breathing in English?

Yes, осознанное дыхание is a common, almost technical phrase in the context of:

psychotherapy
meditation and mindfulness
yoga and breathing exercises

It corresponds closely to mindful breathing or conscious breathing.

The adjective осознанный means realized, consciously understood and intentionally done. So осознанное дыхание implies paying attention to your breath intentionally, not just breathing automatically.

Could we say сознательное дыхание instead of осознанное дыхание? Is there a difference?

You could say сознательное дыхание, and people would understand, but:

осознанное дыхание is the standard collocation in the context of mindfulness, therapy and self-help.
сознательный can mean conscious, deliberate, but also responsible, conscientious in a social or moral sense (e.g. сознательный гражданин – a responsible citizen).

Because of this, осознанное дыхание sounds more natural and specific for the mindfulness idea.

Can the word order in the subordinate clause change, for example …что помогает расслабляться осознанное дыхание?

Yes, Russian allows flexible word order, and you can say:

…что помогает расслабляться осознанное дыхание.

Grammatically this is correct. The meaning is the same, but the focus changes:

…что осознанное дыхание помогает расслабляться.
Neutral order, subject first. Just states the fact.
…что помогает расслабляться осознанное дыхание.
More like: what helps you relax is mindful breathing – emphasis on осознанное дыхание as the answer to the question what helps?

In normal neutral narrative, осознанное дыхание помогает расслабляться is the most common and natural ordering.

Where is the stress in the words of this sentence, and is there anything tricky in pronunciation?

With stress marks:

Психотерапе́вт – psi-kho-te-ráevt (stress on -ре́вт)
сказа́л – ska-zál (stress on -за́л)
что – что́ is stressed as a whole (one syllable)
осо́знанное – o-sóz-na-no-ye (stress on -со́з-)
дыха́ние – dy-há-ni-ye (stress on -ха́-)
помога́ет – po-ma-gá-yet (stress on -га́-)
расслабля́ться – ras-slab-lyá-tsa (stress on -ля́-)

Main things to watch:

психо- at the start of психотерапевт: pronounce пс together, not with a vowel between.
Double сс in расслабляться is just a long s sound; don’t insert an extra vowel.