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.
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.
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.