Does anyone have advice on how to deal with disappointment, when you shouldn't have had expectations to begin with?

I'm at dragon con this weekend (if you're here too, we should hang out!) and I'm having a good time. But this morning, I had my photo taken with a bunch of people that I've always wanted to meet, and I've been looking forward to it for months.

But now it's over, and...nothing. It was hours of waiting for 3 seconds of interaction, and then a photographer shouting to move. Everyone was nice, but now I just feel sort of...empty I guess. Like this thing I've been looking forward to is over, and didn't quite meet my expectations.

But what the hell were my expectations? It's not like I believed that anything would happen beyond a cursory hug for a photo and then on to the next person. So how the hell do I manage to be disappointed when there's nothing to be disappointed about? Does anyone else know how to deal with this?