Well, the theory reminds readers that at the beginning of Grease, Sandy said in “Summer Nights” that Danny saved her life when she nearly drowned.
This especially weird Grease theory (found on Imgur) begins by pointing out how the movie ends with Danny and Sandy leaving the fair in a car that soon breaks the laws of gravity and flies into the air.
As the theory succinctly summarizes: “The entire movie was a drowning woman’s coma fantasy.”
As her brain is deprived of more oxygen, the vision gets more outlandish, until finally, as Danny makes one last attempt to save her, Sandy imagines them flying off in a car together.