Thank to everybody for input. I'm very much appreciated.
Kaddyuk, you are generally right about circadian, excluding some small detail. The word “Circadian” is derived from a Latin, not from Greek.
I'm taking my B1 JAR66 exams at UK CAA (Gatwick). Already done 10 modules. Planning to sit modules 9,10 and Essay on August, 6.
I'm worrying about jet lag, because I'm preparing for Essay exam. As you probably know, Essay paper contains one human factors related question. I've got some sample questions. One of them asking about jet lag.
Again, many thanks to all.
EngOverspeed