First thing that came to mind when I saw the title, was the joke where the punchline is "Your wife's not dead, sir, she's ENGLISH."

@jorgito2001 said:

Interesting fan theory that's sprung up the last few years...and would certainly explain why that car just flew off into the clouds at the end (that ending was ALWAYS super weird to me, even as a kid)

Here's the THEORY in short detail

I just read that... but here's what I think... if we're going in that route.... This cannot be Sandy's dream (she is dead) the dead can't dream. Instead it's Danny's dream. He attempted to rescue her, he wasn't successful, in his attempt she died and he fell into a coma... so while in the hospital and in the coma he dreams all these things.... and at the end when they fly off into the sky that's him coming out of the coma and finally dying... and he is off to reunite with the already dead Sandy.... but since she was always part of his dream.... in the end of the dream they ride up together...... LoL... could this be the reason for their ages not being teens in high school? Because dreams are like that, you dream of people you know and they appear in any situation your dream state puts them in.