tatami no ue ni suwaru to, kimoti ga otitukimasu.

It is read:

たたみ の うえ に すわる と、きもち が おちつきます。

A more natural chunking is:

畳の上に / 座ると、 / 気持ちが / 落ち着きます。

Key readings:

• 畳 = たたみ
• 上 = うえ
• 座る = すわる
• 気持ち = きもち
• 落ち着きます = おちつきます

No. This と is not the and particle.

Here, と is a conditional marker, meaning something like:

• when
• whenever
• if

In this sentence, it expresses a natural or regular result:

• 畳の上に座ると = when/whenever I sit on tatami

A good way to think about it is:

• Action 1 happens
• then Action/State 2 naturally follows

So the nuance is not just a one-time event. It sounds like a general tendency: sitting on tatami has a calming effect.

Because the clause before と normally uses the plain form.

So:

• 座ると is the standard pattern
• the main sentence ends politely with 落ち着きます

This is very common in Japanese:

• subordinate clause = plain form
• main clause = polite form if the speaker wants polite speech overall

Using 座りますと is possible in very formal Japanese, but it sounds much stiffer and less common in everyday speech.

The particle に marks the place where someone ends up sitting.

With verbs like 座る,

• に often marks the location you sit onto / in / at
• compare:
  • 椅子に座る = sit on a chair
  • 床に座る = sit on the floor

So:

• 畳の上に座る = sit down on top of the tatami

A helpful contrast:

• に often marks a destination or resulting location
• で often marks where an action takes place

For example:

• 畳の上で食べる = eat on the tatami
• 畳の上に座る = sit down on the tatami

Yes, you can.

• 畳に座る is natural and common
• 畳の上に座る is a little more explicit

The phrase の上 literally means on top of / on the surface of.
So 畳の上に座る emphasizes the physical surface a bit more.

In many situations, both are fine:

• 畳に座る
• 畳の上に座る

The version with の上 can feel slightly more descriptive.

Here, 気持ち means something like:

• feeling
• mood
• state of mind

It does not have to mean one specific emotion like happiness or sadness. In this sentence, it refers more broadly to your inner feeling or mental state.

So 気持ちが落ち着きます means your feelings or mood become calm/settled.

Because 気持ち is the subject of 落ち着きます.

The verb 落ち着く means:

• to calm down
• to settle
• to become composed

So the thing that becomes calm is 気持ち.

That is why が is natural:

• 気持ちが落ち着きます = the feelings settle down

If you used は, the nuance would change. は would make 気持ち the topic, often with contrast or emphasis.

For example:

• 気持ちは落ち着きますが、足が痛くなります。 = As for my feelings, they calm down, but my legs start to hurt.

So in the original sentence, が is the straightforward choice.

Because 落ち着く and 落ち着ける are different verbs.

• 落ち着く = intransitive
  to calm down / to become settled
• 落ち着ける = transitive
  to calm something down

In this sentence, the feeling itself becomes calm, so Japanese uses the intransitive verb:

• 気持ちが落ち着きます

If you used 落ち着ける, you would need something that causes the calming more directly, such as:

• 音楽が気持ちを落ち着けます。 = Music calms my feelings.

Japanese often leaves that unstated.

This sentence could mean:

• I feel calm when I sit on tatami
• You feel calm when you sit on tatami
• People feel calm when they sit on tatami

Context decides.

Also, Japanese often omits the possessor of body parts and mental states. So 気持ちが落ち着きます does not literally say my feelings or your feelings, but that is understood from context.

It usually sounds like a general tendency.

Because of dictionary form + と, the sentence has a habitual or natural-result feeling:

• Whenever I sit on tatami, I feel calm
• Sitting on tatami makes me feel calm

If you wanted to talk about one particular occasion, Japanese might use a different structure depending on the nuance, such as たら or simply describe the event directly.

So this sentence sounds like a repeated experience or a general truth.

The comma is mainly for readability and rhythm.

It separates:

• the conditional part: 畳の上に座ると
• from the main statement: 気持ちが落ち着きます

Japanese commas are often more flexible than English commas.
So the comma here is natural, but the sentence could also be written without it:

畳の上に座ると気持ちが落ち着きます。

Both are fine.

Literally, 上 means up, above, or top/surface.

But in phrases like A の 上, it often means:

• on
• on top of
• on the surface of

So:

• 畳の上 = on the tatami / on top of the tatami

In natural English, you usually would not translate it as the upper part of the tatami. Here it simply means the surface you sit on.

Japanese often describes changes in terms of what part of you changes.

So instead of saying:

• I become calm

Japanese may say:

• my feelings calm down
• my heart settles
• my mood becomes calm

That is why expressions like these are common:

• 気持ちが落ち着く
• 心が落ち着く
• 気分が落ち着く

This style can sound very natural in Japanese, even if English would often use I feel calm instead.