"Tomorrow something's going to happen to you

"明天你会碰到件事
and that thing is going to be simply fantastic,

这件事非常好
absolutely incredible, absolutely wonderful."

好得难以置信不可思议"
And you said,

然后你说
"Well, I believe you and I have to tell you,

"好吧我相信你但我要告诉你
I'm just filled with dread and foreboding in thinking about it."

我一想到这件事就觉得担忧害怕"
That wouldn't make any sense at all.

这完全不合情理
It makes sense to be filled with dread or foreboding or what have you only

你感到担忧害怕
if the thing you're looking forward to,

只有当你想到的事情
anticipating, is itself bad.

本身是坏事时才合情理
Maybe, for example,

例如
it makes sense to dread going to the dentist,

你害怕去看牙