Parliament-Funkadelic Robbed

Shaunna Hall tells TMZ ... the $5,000 guitar was stolen from the P-Funk tour bus, in Memphis, on August 5. But what REALLY sucks is ... the instrument was specifically designed to accommodate a painful physical affliction she sustained after a bad accident last year.

Hall says her neck and shoulder were injured in the accident -- and ever since the incident, traditional wood guitars are simply too heavy for her to play for several hours at a time.

We're told the custom guitar is made from carbon fiber -- weighing a mere 4.5 pounds -- which puts less stress on her sensitive neck and shoulder ... helping her endure performing a full concert.