The obligation to continue saying the story of the exodus:[1]

After the Seder one is obligated[2] to discuss and deal with the laws[3] of Pesach and the story of the Exodus, telling over the miracles which G-d has done for our ancestors, until sleep overcomes him. [This means that once one begins feeling himself dozing off, he may say Kerias Shema and go to sleep.[4] Nevertheless, one who fights falling asleep in order to increase in the Mitzvah of saying the story of the exodus, is praised.[5] One who finishes the Seder before midnight is at the very least to push himself to be awake until midnight.[6] Some Gedolei Yisrael were accustomed not to go to sleep regularly on this night, and rather would fall asleep in their chair.[7] Once one falls asleep, he is no longer obligated to continue saying the story even if he wakes up before Alos.[8]]

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[1] Admur 481:1; Michaber 481:2; Rosh 10:33; Tur in name of Tosefta Pesachim 10:8; Shlah Hakasdosh; See Haggadah of Rebbe “Mitzvah Aleinu”; Nitei Gavriel 105; See Kaf Hachaim 481:11 that one is to be awake until midnight and may then go to sleep; Kaf Hachaim 481:10-11; Piskeiy Teshuvos 481:2

[2] Vetzaruch Iyun from the story and wording brought in the Haggadah and Tosefta ibid “Vechol Hamarbeh Harei Zeh Meshubach” which implies one is not obligated to do so. See alos Or Tzadikim 32 “It is a proper custom to be awke the night of Pesach.” Perhaps, however, one can explain that this means that whoever pushes himself to not drift to sleep in order to increase in the story, is praised, however until one has the urge to sleep he is obligated to say the story. [See Chok Yaakov 481:2; Chasdei David on Tosefta ibid; Nitei Gavriel 105 footnote 1-2]

[3] See Drushei Chasam Sofer p. 265 that one is not Yotzei with Pilpulim in Halacha but only with stories and Halacha Pesuka

[4] See Nitei Gavriel 105 footnote 1; 106 footnote 3 and previous and next footnotes; See also Siddur Yaavetz that if one is weak and the like, and if he does not sleep he will be unable to Daven properly the next day, then he may go to sleep

Other opinions: Some Poskim rule one is required to say the story of the exodus until he literally falls asleep. [Hisorerus Teshuvah 273]

[5] Chasdei David on Tosefta ibid; See Chok Yaakov ibid and previous footnote

[6] Kaf Hachaim 481:11 based on Zohar

[7] Leket Yosher p. 106 that so was the custom of the Terumas Hadeshen; Chasam Sofer; See Nitei Gavriel 105:2

[8] Implication of Admur ibid “After drifting to sleep he may drink”; Chok Yaakov 481:1; P”M 471 A”A 1; Piskeiy Teshuvos 481:2

Other opinions: Some Poskim rule one is required to say the story of the exodus even after he awakens. [Hisorerus Teshuvah 271]