"幸福来的太突然" 英语怎么说?

Happiness suddenly falls on(strikes也可以）me, which is so unimaginable to me that I am afraid it is just in a flash.

in a flash 昙花一现

刚才我把它翻成了一句话 如果你硬要按中文的短句格式翻成3句 也可以这样：Happiness suddenly strikes me.
Even I myself cannot expect it.
But I am afraid it is just in a flash

但是我自己认为翻成一句更好。

幸福来的太突然Suddenly,my happiness comes
连我自己也没想到Even I haven't expected it
但我担心它太短暂But I am afraid that it can not last long

This happiness arrived so quickly. Even I coulld've never expected it. I am afraid, however, that it won't last long.

All of a sudden the happiness came without being expected even by myself.
However, I'm worried that is might just be somewhat temporary.

Happiness comes suddenly
i am not even expecting it
but i am afraid that it is temporary.