Multiple female characters experience attacks of hysteria. Most modern mental illness diagnoses didn't exist at the time of writing, but it wouldn't be a stretch to consider several characters to be mentally ill.
In one chapter close to the end, a character experiences hallucinations, but these are clearly described as unreal and even the character himself recognises that he is hallucinating.
A mentally disabled woman is raped. A baby with polydactyly is neglected. A lot of ableist language (cripple, hunchback, imbecile, etc.) though generally not used in a derogatory context.