Okay, well I think I figured out how this long hair could've possibly grown overnight. I'm guessing it was an ingrown hair, and since all the other hairs on my neck are clear and very small, this one must've kept growing inside because it never broke through the skin, so it didn't know when to stop growing. I've been skin brushing everyday, and I brush a few times down my neck, so this could've opened up the pore, causing the long hair to come out.
Problem solved :). On to the more serious problems out there...