Am I going crazy? I saw a ghost and I'm freaked out!!!?

First of all, people should never taunt spirits. Secondly, sounds like your friend Ryan is a non-believer and he's heard that hype about the mass hallucination thing, which is bogus, and has fallen into the same trap as the other non-believers. Although it could be used in other situations, when other people see the exact same thing at the same time, it cannot be called that. If in fact you did see that, then you've seen a ghost, and now you can join the ranks of the rest of us who've seen them. And, as you can see, they're nothing to be afraid of. But, don't let this Ryan guy get to you, he's just ignorant to it at this time.