I have read a few books about the Civil War, and it's usually mentioned that in the South there was a tremendous fear and paranoia of a slave rebellion. It seems unlikely the slaves could have ever rebelled to any significant degree, give the way they were controlled and the swiftness in which the South would have put down any nascent rebellions. So what was this fear based on?
It was not entirely paranoia, it was based on actual events that happened. Namely, most of this came from the Haitian Revolution in the 1791-1804 made slave-owners uncomfortable because it was a successful slave revolt and they weren't able to stop the information about it from being spread.
As knowledge of the uprising in Haiti became common knowledge, two things happened. First, whites in the south started to become paranoid that slaves would try to do the same and in some areas, the slaves were in such great number that they might have had a good chance if they got organized. And second, some slaves and abolitionists actually did organize and attempt revolts. There were several of these,the most well-known probably being Gabriel's Rebellion in 1800 and Nat Turner's slave rebellion in 1831 and Denmark Vesey's Consipiracy to rebel in 1822.
These attempts only reinforced the fear and paranoia of a rebellion among whites. Keep in mind that in the years before the Civil War, the slaves made up about half of the population of the lower south and about 1/3 of the population of the upper south. Those are significant enough numbers to make the fear of a wide-spread uprising seem not far fetched.
PhD in Sociology with BA in Black Studies and History here:
Your use of the word "paranoia" is telling. Although violent, armed slave rebellions did occur in the South, they were EXTREMELY rare and usually ended very quickly. Fear of slave rebellions was largely based on paranoia, not on evidence that they happened all the time. Think of how afraid we (Americans) are of Islamic extremist terrorism today, but how rarely these events actually take place in our country. Now imagine that most news was spread word-of-mouth, so that exaggerations were super commonplace. Paranoia takes off big time.
More common were small acts of rebellion: breaking farm tools "on accident," feigning illness, acting stupid, poisoning farm animals, etc. Anything to slow down production without being blamed for it. This was an effective strategy for slaves, plus it went largely undetected by slave-owners. In adjusted dollars, it probably cost slaving families millions of dollars in lost income. But these were not open "rebellions." Those existed more in the minds of paranoid Southern Whites than in the fields of the South.