None of this is real!

What really separates a dream from reality?
I'm never certain of anything I think is real
Sometimes I stare into the ceiling at 2 AM, numb, unable to move.
I don't remember any of what happens after that.
The next morning, I stare at the same ceiling brightly lit with daylight.
Now how do I know if I ever slept because I wake up tired with a splitting headache.
What if I never woke up?
Maybe I'm stuck in a dream.
Maybe we are all stuck in a dream.
What if none of this is real?
What if...?