What does Isaiah mean when he says that the twilight he longed for turned into trembling?

Isaiah continues to describe his emotional reaction to the vision he received. The twilight I longed for may well be literal: where he usually enjoyed the evening as a time of rest, the terrible vision he saw stayed with him so that the evening time turned into a time of dread. However, it is equally plausible that Isaiah meant it figuratively: the twilight time signals the end of the oppressors' power. He has longed for it, but then he saw the horrors that the judgment on Babylon would entail.