Interesting question! In the book The Slave Dancer by Paula Fox, Jessie is afraid of a slave uprising.
When the slave ship arrives at the coast to load the slaves, Jessie learns that he might carry a gun. Subsequently, his fellow crewmate tells Jessie that the slaves might have an uprising while they can still see their homeland. As Jessie's crewmate reveals:
“If the blacks try anything, it’ll be then, when they can still see where they come from. Oh, they’ve done terrible things I could tell you about! Killing a crew and a master and all, then flinging themselves back into the sea, even shackled!”
After his fellow crewmate shares this information, Jessie begins to think about the stories he heard about slave uprisings at home. When Jessie was at home, he heard about uprisings occurring in other states, such as South Carolina and Virginia.
Consequently, these events made Jessie afraid of a slave uprising. After hearing about stories from his fellow crewmate and remembering stories from back home, Jessie becomes nervous.