Why are Tom's nightmares significant?

Tom's nightmares represent his unsettled guilt and fear. stemming from his withholding of the truth. Dreams are often an outlet for one's unconscious; we can often gain more insight into the nature of a character through the analysis of his or her dreams. Here, Tom's conscience is manifested in his nightmares because it is the only time his fears are allowed to enter his mind; his fear of Injun Joe and his vow with Huck are impedances to his feelings of guilt. Just as before on Jackson island, when Tom was unable to fall asleep, his conscience haunts him. As part of growing up and assuming responsibility, Tom must learn to listen to his conscience rather than ignore it.