Why did Jess awake with a feeling of dread on Wednesday night?
In Chapter 11, after waking from a nap on Wednesday night, Jess feels overwhelmed with a vague sense of dread because he partially remembers that his best friend Leslie has just died. Her death seems to him like a frightful dream, something that he surely imagined and something that could never truly happen, and yet the feeling that she may have actually died is gnawing on Jess's subconscious.
Earlier that day, he'd heard the news of Leslie's death, but he'd reacted with strong disbelief. It is this disbelief mixed with the dreadful realization that Leslie may actually be gone that bothers Jess in his half-awake, groggy state:
It came into his mind that someone had told him that Leslie was dead. But he knew now that that had been part of the dreadful dream. Leslie could not die any more than he himself could die. But the words turned over uneasily in his mind like leaves stirred up by a cold wind. If he got up now and went down to the old Perkins place and knocked on the door, Leslie would come to open it, P. T. jumping at her heels like a star around the moon.
Still, as Jess wakes up, he tries to push the idea of Leslie's death out of his mind, trying to convince himself that it's impossible. He imagines how he'll go and find her, how they'll visit Terabithia together, and how he'll apologize for failing to invite her along on his trip to Washington with Miss Edmunds. As readers, we sadly witness Jess's denial of Leslie's death.