Learn Hardcore Russian: Иногда мысль помогает мне расслабиться.

this shifts the meaning to Sometimes (my) thoughts help me relax — emphasizing multiple thoughts, or the general flow of thoughts, rather than a single one. Both are grammatically correct; it’s just a nuance of meaning.

What case is мне, and why is it used here?

Мне is in the dative case (from я → мне).

The verb помогать / помочь (to help) in Russian takes the dative for the person who is being helped:

помогать кому? — to help whom? → мне, тебе, ему, ей, нам, вам, им

So in the sentence:

мысль помогает мне расслабиться

literally: a thought helps *to me to relax, i.e. *a thought helps me relax. The dative мне is required by the verb помогает.

Why is it помогает мне расслабиться and not something with a preposition, like помогает мне, чтобы расслабиться?

Russian doesn’t need a preposition like English “in order to” here.

The pattern помогать кому-то + инфинитив is completely standard:

Это помогает мне учиться. – This helps me study.
Спорт помогает людям жить дольше. – Sport helps people live longer.

So помогает мне расслабиться is exactly the natural Russian structure.
Чтобы is used when you want to express purpose in a separate clause:

Я думаю о приятном, чтобы расслабиться.
I think about pleasant things in order to relax.

Here that’s not needed; the infinitive alone after помогает is enough.

What is the infinitive расслабиться exactly? Why does it end in -ся?

Расслабиться is a reflexive, perfective infinitive:

base verb: расслабить – to relax (something/someone)
reflexive form: расслабиться – to relax oneself, to become relaxed

The -ся ending marks the reflexive form, where the action turns back on the subject:

Я расслабляю мышцы. – I relax (my) muscles. (non‑reflexive)
Я расслабляюсь. – I relax (I “relax myself”). (imperfective)
Я хочу расслабиться. – I want to relax (become relaxed). (perfective)

In the sentence, расслабиться means to become relaxed, with the action affecting the same person who acts.

Why is the perfective form расслабиться used, and not the imperfective расслабляться?

After verbs like помогать (to help), both aspects are possible, but they give slightly different nuances:

помогает мне расслабиться – helps me (to) relax, focusing on reaching the relaxed state (a more goal/endpoint-oriented view).
помогает мне расслабляться – helps me (with the process of) relaxing, more about the ongoing activity.

In many contexts, especially for “help me relax” as a result, расслабиться (perfective) feels more natural.
Расcлабляться would sound more like it helps me engage in the activity/habit of relaxing.

Could I say Иногда мысль помогает расслабиться and drop мне?

Yes, that’s grammatically correct and quite natural.

Иногда мысль помогает расслабиться.

This sounds more impersonal and general: Sometimes a thought helps (one) relax / helps (you/people) relax. The subject мысль remains, but the person who relaxes is left unspecified — it’s understood as “someone, people in general”.

With мне, the sentence is specifically personal:

Иногда мысль помогает мне расслабиться. – Sometimes a thought helps *me relax.*

Why is мысль feminine when it ends with a soft sign (ь)? How do I know its gender?

Nouns ending in -ь can be either masculine or feminine; you have to learn the gender with the word.

Мысль is feminine. You can see that from:

Its adjective agreement: глубокая мысль (a deep thought) — -ая ending for feminine.
Past tense with it as subject:
Эта мысль мне очень помогла. – This thought really helped me.
The verb помогла is feminine.

So, when you learn the noun, remember it as:
мысль (ж.) – feminine.

Could I say одна мысль instead of just мысль? What’s the difference?

You can, but the nuance changes.

Иногда мысль помогает мне расслабиться.
= Sometimes a thought helps me relax. (generic “a thought”)
Иногда одна мысль помогает мне расслабиться.
Literally: Sometimes one single thought helps me relax.
Here одна emphasizes that just one particular thought is enough — it sounds more expressive, almost like “just one thought is enough to calm me down sometimes.”

So одна мысль adds emphasis on “one, just one”, rather than just “a thought” in general.

Can иногда go to a different position in the sentence, like in English?

Yes. Common options:

Иногда мысль помогает мне расслабиться. – neutral, very natural.
Мысль иногда помогает мне расслабиться. – similar meaning; “мысль” is slightly more in focus.
Мысль помогает мне иногда расслабиться. – possible, but here иногда often feels more attached to расслабиться (sometimes I get to relax), and the rhythm is a bit less natural.

The most typical, neutral choice is exactly what you have: Иногда at the beginning.

How would the sentence change if I used думать instead of мысль?

You’d need to change the structure, because думать is a verb (“to think”), while мысль is a noun (“a thought”).

Original:

Иногда мысль помогает мне расслабиться.
Sometimes a thought helps me relax.

With думать, you could say:

Иногда думать о хорошем помогает мне расслабиться.
Sometimes thinking about good things helps me relax.

Here думать (о хорошем) acts like “thinking (about good things)”, and it is what helps you relax. The grammar changes, but the general idea can be kept.