Simplify the following text for a Grade 7 native English-speaking person.
Original: In psychiatry , dysaethesia aethiopica was an alleged mental illness described by American physician Samuel A. Cartwright in 1851 , which proposed a theory for the cause of laziness among slaves .
Simplified: Dysaethesia Aethiopica was a term to describe a mental illness which was believed to be why Afro-American slaves were lazy . American physician Samuel A. Cartwright described the condition in 1851 .