Is frequent supplication during "Qiyam Al-Layl" (night vigil prayers) considered to be from the "self" (nafs), and is occasional, simple supplication also from the "self"? And what is the meaning of that?

The periods of enthusiasm and inclination towards worship and supplication you experience sometimes, and then languor and laziness at other times, are a natural phenomenon affecting most people. The human soul experiences periods of zeal and decline. The Prophet (peace and blessings of Allah be upon him) clarified this by saying: "Indeed, for every deed there is a period of zeal, and for every period of zeal there is a period of slackness. So, whoever's zeal is directed towards my Sunnah, he has succeeded. And whoever's period of slackness is directed towards other than that, he has perished." Therefore, moderation is advised, and it is best to avoid extremism and negligence in both states.