Body dysmorphic disorder. And you are right. People go to South America and pay $20,000 to have their arm or leg removed and then come back here and you go on disability. Disability isn’t the reason they do it but it is what they end up on
I read about an even more disturbing delusional disorder a while ago, I'll see if I can find the link and post it later. Basically, you have able-bodied people who are convinced that they are disabled people mistakenly born into able bodies. They insist on using crutches and wheelchairs even though they don't need them, or in more extreme cases attempt to break their spines (or go overseas to get their lower spines severed) so that they can realize their "true identity" as paraplegics.
Again, this isn't so different from transsexuality.