A couple of things - first of all, where are you coming from? Different jurisdictions have different rules for disability payments and benefits. If you're travelling within the EU, it's a whole different situation than if you're coming from outside, too.

Then there is the matter of whether you are looking to have your disability benefits sent to you in Spain during your visit there, or if you're ok with having them applied to your bank account back home. Transfering your payments elsewhere implies a transfer of your residence, and that's much harder to manage than a simple visit of a few months.
Cheers,
Bev