I was thinking of Schopenhauer. And it's actually pain rather than terror, which should make us all feel a bit better.
I suppose he would argue that happiness is transitory, as is terror (usually).
“The basis of all willing is need, lack, and hence pain, and by its very nature and origin it is therefore destined to pain. If, on the other hand, it lacks objects of willing, because it is at once deprived of them again by too easy a satisfaction, a fearful emptiness and boredom comes over it; in other words, its being and its existence itself becomes an intolerable burden for it. Hence life swings like pendulum to and fro between pain and boredom, and these two are in fact it has ultimate constituents.” (The World as Will and Representation)
I suppose he would argue that happiness is transitory, as is terror (usually).
“The basis of all willing is need, lack, and hence pain, and by its very nature and origin it is therefore destined to pain. If, on the other hand, it lacks objects of willing, because it is at once deprived of them again by too easy a satisfaction, a fearful emptiness and boredom comes over it; in other words, its being and its existence itself becomes an intolerable burden for it. Hence life swings like pendulum to and fro between pain and boredom, and these two are in fact it has ultimate constituents.” (The World as Will and Representation)