Am I obligated to fulfill my vow of not sleeping from after Fajr prayer until sunrise for the rest of my life, or is it permissible for me to stop and feed ten needy persons?

If you repent sincerely after committing a sin, Allah Almighty will accept your repentance. As for the vow (nathr), if your intention behind it was to strive against your ego and fill your time with worship (obedience), then you are obligated to fulfill it as long as you are able, even if it involves hardship. However, if your intention was to punish and torment yourself, this is not a legitimate religious objective, and it is not permissible to fulfill such a vow, as the Prophet (peace be upon him) said: "Whoever vows to obey Allah, let him obey Him; and whoever vows to disobey Allah, let him not disobey Him."