I'm not saying it's an overactive imagination, nor that what you believe you saw you genuinely believe you saw without any bias, it's just not convincing enough an argument for me to suddenly start believing in ghosts because my counter argument in my head is much stronger and until I see one myself, I'll probably always be the same.
People can be mistaken, then, especially with secptics, you can start to make yourself believe more by adding details that weren't necessarily there.
I don't think it's a massive coincidence that most people see ghosts at night, when they're half asleep. But again, that's my logic as a sceptic. If you saw a ghost you saw a ghost, you've no need to convince me or anyone.