Is it common to skip a month of menstruation or have it for more than two weeks?

I skipped my period for a month before.

The following month, I had my period for about 20 days.

As soon as my period ended, I hurriedly visited the hospital after hearing to come visit once it was over.

But I seriously wonder if I have some kind of serious illness...

They just brushed it off as if nurses and doctors are nothing special.

Since I had irregular periods when I was young, I thought it was just normal.

I was scared because the 20-day menstrual cycle is my first time experiencing it.

It makes me wonder if it's really nothing after all...

Is this a common situation?