It's February 1,st today.

I am going back to amy normal life, as before.

I traveled from China to central Canada, crossing 14 time zones, and just recovered from the jet lag yesterday.

Adding "the" is optional really but slightly more common from how I've heard most native English speakers talk about jet lag. When they're talking about their own experiences of jet lag, they say stuff like "the jet lag was so bad when I got back".

It's interesting to learn that it is normal that weo need a day to adjust to one time zone differences when traveling by plane.

I've heard that sometimes it takes many days to adjust if the time zone difference is big.

If you wanted to emphasize that even a single hour of time zone difference makes an impact, you could say:

"It's interesting to learn that it is normal to need a day to adjust to a time zone difference of even just one hour when traveling by plane."

In the initialfirst few days, I always felt fatigued during the days while having insomnia in theat nights.

Because you already said "In the initial days" at the start of the sentence, it is more natural to just say "during the day" and "at night" instead of reiterating that you had fatigue and insomnia over multiple days and nights.

HThe human internal clock is really magical, but it also can sync with the local times through sleeping.

I don't understand the use of "but" here, because the two clauses you wrote don't seem like they contradict each other in any way. I would probably write it more like this:

"The human internal clock is really magical. It can sync with the local time just by sleeping."

Jet lLag

It'Today is February 1, todayst.

I am going back to amy normal life as before.

I traveled from China to central Canada, crossing 14 time zones, and justdifferent time zones. I recovered from jet lag yesterday.

It's interesting to learn that it is normal that we need a day to adjust to onea time zone difference when traveling by plane.

In the initial daysbeginning, I always felt fatigued during the days while having and had insomnia during the nights.

HThe human internal clock is really magical, but also and can sync with local times through sleeping.

Jet lLag

Title capitalization

It's February 1, today.

In the initial daysitially, I always felt fatigued during the days while having insomnia during the nights.

HThe human internal clock is really magical, but it can also can sync with local times through sleeping.