The first thing a Jew says on waking is a single sentence, said in bed, before getting up and before washing: Modeh ani lefanecha, melech chai vekayam, shehechezarta bi nishmati bechemla, rabba emunatecha. “I give thanks before You, living and eternal King, for You have returned my soul within me with compassion; great is Your faithfulness.”
A sentence with no Name
None of the Divine Names appears in it. That is why the halachic authorities allow it to be said before the hands are washed, when a person may not yet mention a Name (see the Mishnah Berurah, Orach Chayim 1). The text is not in the Talmud. It appears in sixteenth-century sources from Safed, such as Seder HaYom, and was accepted in nearly every community.

Sleep and the soul
The Sages call sleep one sixtieth of death (Berachot 57b). The Kabbalists understood the night literally enough: the soul leaves the body and rises, and a person wakes because it has come back. Modeh Ani is the first thing said on its return. The levels of the soul and their connection to the worlds are described in the article on the five levels of the soul.
The closing words, rabba emunatecha, come from a verse in Eichah (3:23): “They are new every morning; great is Your faithfulness.” The Midrash reads it this way: because You renew us every morning, we know that Your faithfulness is great (Bereshit Rabbah 78:1). A person who wakes has been given something back, and the sentence says so.
What comes next
The sentence takes a few seconds and needs no preparation. The next step is the washing of the hands, covered in Netilat Yadayim, and then the blessing for the body, Asher Yatzar. Gratitude as a practice runs through the whole morning and is the subject of Gratitude, Devekut and Inner Peace.