Because the verb here is fermarsi, which often means to stop in the sense of to stop oneself / to come to a stop.
So:
The mi is the reflexive pronoun that goes with fermarsi.
Italian often uses a reflexive form where English just uses a normal verb. So although English says I stop, Italian commonly says mi fermo.
The infinitive is fermarsi.
Here is the present tense:
In your sentence, mi fermo is the first person singular: I stop.
Because Italian expresses sensations like being cold, being hot, being hungry, and being thirsty with avere (to have), not essere (to be).
So:
If you say sono freddo, it usually means I am a cold person/object or my manner is cold, not I feel cold.
Because Italian often uses the present tense in the same situations where English also uses the present:
This sentence sounds like a general statement or something happening right now. Italian does not need a special progressive form here.
If needed, Italian can use stare + gerundio for an ongoing action, but it is not necessary in this sentence.
Yes, but it changes the feel slightly.
In most cases, mi fermo is the more natural and simpler choice here.
Mi sto fermando puts extra emphasis on the action happening right now.
It is the most natural and common choice.
You could also find other conjunctions such as:
But they are different in tone or structure:
For everyday spoken Italian, perché is usually best.
Yes. Italian word order is flexible, though some versions sound more natural than others.
Your sentence:
A natural variation would be:
Both are correct. Starting with Dopo tre vasche puts more focus on after three lengths.