Hmm, this sounds sort of normal to me -- I am not sure if I will phrase what I mean the way I want, but here goes.

I very often find that I dread an event beforehand more than I am bothered by the event itself. If I have plans to see someone I don't want to see, I will spend a ridiculous amount of time worrying about it... and then when I see the person, those worries go away while I am busy actually seeing them/dealing with them... and then when I get back home, I might be happy I saw them or back in aggravation mode.

There might be a slight irritation while I am doing the thing that I was dreading, but the irritation is not half as strong as the dread. That may not be the same as your 'nothing' that you felt, but this seems sort of similar to me.

I just figure that when I am by myself, I have time to dwell/ruminate. When I am with other people, I have to concentrate on something else and can't dwell.