So far the anticipation has been worse than the actual event. Build-up, concern, etc ahead of time have all been way out of proportion. In the moment, surprise, wonder, and curiosity ... and humor ... have proven to be the real substance when I've seen one. That's true most of the time when there were pretty strong indications they were around though not seen as well, however, a couple of those times have also been pretty terrifying.
We bring a lot to the table with us, state of mind at the moment, basic comfort in whatever the environment is, awareness / knowledge of their existence, and if we think about them at all, what we believe. Those all predispose us to one sort of emotional response or another. Sometimes we tell ourselves stories about how we'll react that prove untrue and sometimes being confronted with that untruth is more disturbing than the event itself.
MIB