>>>>That's not the same. Invalid is a disabled person - check in other languages. "Bolesnik" is just a person with an illness.
>>>
>>>There's always "sufferer": "... The later stages of this disease can bring great pain to the sufferer ..."
>>
>>...which doesn't imply he's ill. He may just be gently interrogated: "... The later stages of this technique can bring great pain to the sufferer ..."
>
>I'd've thought that the word "disease" in the sentence did!

So "sufferer" isn't ill until you specify disease. Therefore not a good translation.