This episode is always an uncomfortable one for me to sit through because it's about fear, and core fear - the fear you don't want anyone else to know grips you in the middle of the night. What if suddenly everyone could see, nay experience, what you feared most? There's some kind of fear in that too - the being stripped naked and judged by what you fear. And the two fears that I really relate to in this episode are Buffy's - becoming that which you most hate (whatever that may actually be) and Willow's. In fact, when I was learning to get over my own fear of public speaking, I once gave a speech that included this very thing - Willow's fear of singing in public from this very episode.
I love this episode but it's not one I enjoy sitting through - there's spiders and clowns and permanent night and *shiver*