gamansisugiru to, huanna kimoti ga sukosizutu tamatte ikimasu.

しすぎる comes from 我慢する (to endure/hold back) + すぎる (to do too much).

• The verb する changes to its ます-stem form し
• Then you add すぎる → しすぎる = to endure too much / to overdo the self-restraint

So grammatically it’s:

• 我慢する → 我慢し + すぎる → 我慢しすぎる
• Meaning: “if you hold it in too much,” “if you overdo suppressing yourself,” etc.

In this sentence, と is not the quotation と. It’s the conditional と, which means roughly “when / if / whenever”.

• 我慢しすぎると、～
  → “When you endure too much, …” / “If you keep holding it in too much, …”

This と often expresses a natural or inevitable result:

• ボタンを押すと、ドアが開きます。
  “If/when you press the button, the door opens.”

Similarly:

• 我慢しすぎると、不安な気持ちが少しずつたまっていきます。
  “If/when you endure too much, anxious feelings gradually build up.”

So: it’s a conditional marker, not a quotation marker.

Both are possible, but there is a nuance difference:

• 不安が少しずつたまっていきます。
  → “Anxiety gradually builds up.” (treats 不安 as the thing itself)

• 不安な気持ちが少しずつたまっていきます。
  → “Anxious feelings gradually build up.”

気持ち means “feeling” or “emotion.” By saying 不安な気持ち, the sentence:

• sounds more personal and emotional
• emphasizes the inner feeling rather than an abstract “anxiety” as a concept

In everyday speech, 不安な気持ちが… feels softer and more about what’s going on inside someone’s heart/mind.

Because 不安 here is a な-adjective, not just a noun.

• な-adjectives modify nouns with な:
  • きれいな人 (a beautiful person)
  • 元気な子ども (a lively child)
  • 不安な気持ち (an anxious feeling)

Using の (不安の気持ち) would sound unnatural here. When you want to say “an anxious feeling,” you treat 不安 as an adjective: 不安な + 気持ち.

が marks the grammatical subject of the verb たまっていきます:

• 不安な気持ちが少しずつたまっていきます。
  “Anxious feelings (subject) gradually accumulate.”

If you said:

• 不安な気持ちは少しずつたまっていきます。

it would put contrast or topic focus on “anxious feelings” (as the topic), possibly implying “as for anxious feelings (as opposed to something else), they accumulate…” That’s a slightly different nuance.

Here, the sentence is simply explaining what builds up, so が as a neutral subject marker is natural.

• 少し by itself = “a little,” “a bit.”
• 少しずつ = “little by little,” “gradually,” “bit by bit.”

ずつ indicates distribution over time or space, so 少しずつ implies repeated small increases:

• 少しずつたまっていきます。
  → “They gradually build up (a little at a time).”

If you said:

• 不安な気持ちが少したまっていきます。

it could be understood, but it sounds less natural and loses the clear “step‑by‑step accumulation” nuance that 少しずつ provides.

たまっていきます is:

• たまる (to accumulate, to build up)
  → te-form: たまって
  
  • いく (here as an auxiliary)
    → polite form: いきます

So:

• たまっていく = “to go on accumulating,” “to keep piling up,” “to gradually build up (as time goes on).”

Nuance:

• たまる = simply “to accumulate” (a state/event)
• たまっていく = emphasizes a process over time, the ongoing increase into the future.

Thus, 不安な気持ちが少しずつたまっていきます。 focuses on the gradual, continuing build‑up of the feelings.

Vていく often means that an action or state develops or continues from now into the future or away from the speaker’s current point in time.

Common nuances:

• Gradual change:
  
  • 暗くなっていく = “to get darker and darker (going forward)”
• Continuing process:
  
  • 勉強を続けていく = “to keep on studying (from here on)”

In this sentence:

• たまっていく
  → “(the feelings) keep piling up as time passes,”
  → “they go on accumulating.”

So Vていく adds a time/progression feeling compared to just Vる.

Yes, this is normal and grammatical.

• In conditionals like X すると、Y ます, it’s common to have:
  • plain form before と (or たら, ば, etc.)
  • polite form in the main clause

Examples:

• ボタンを押すと、ドアが開きます。
• 勉強しないと、テストで困ります。

So:

• 我慢しすぎると、不安な気持ちが少しずつたまっていきます。

fits the usual pattern: plain conditional clause + polite main clause. The politeness is determined primarily by the final verb form (いきます).

You could say:

• 我慢しすぎたら、不安な気持ちが少しずつたまっていきます。

It’s grammatical, but the nuance shifts a bit.

• X すると、Y often expresses a natural, almost automatic result or general rule.
• X したら、Y is a more general “if/when X happens, Y,” and can sound more event-like or one-time.

In this context:

• 我慢しすぎると suggests a general tendency / predictable consequence: “When people overdo enduring things, anxious feelings (tend to) build up.”

• 我慢しすぎたら can sound a bit more like: “If/when you happen to have endured too much on some occasion, then your anxious feelings build up.”

Both are understandable, but と fits the idea of a general psychological pattern especially well.