Huitzilopochtli appears in front of you and explains the situation.
Human sacrifice rates have gone down in the past millenium, for some reason, and now the Sun is running on emergency power reserves. If something isn’t done, the Sun will become dim enough for the Obsidian Butterfly and her army of Tzitzimimeh, the skeletal women whom all humanity is descended from and have rattlesnakes for penises, to destroy it.
Until they have a proper source of BLOOD to power the Sun, they have to rely on randomly selected human beings to be killed so that the Earth doesn’t freeze to death. This is where you come in.
Now that you have been chosen to die for a noble cause, you can pick your method of being sacrificed, any form of death is acceptable as long as you die within 6 hours (Earth time, not from your perspective). If you don’t choose your method of death by 6 hours, he’ll just rip out your heart.