Rey Mysterio's second WWE Wellness Policy violation has generated a lot of chatter among the wrestlers that drug test failures are mysteriously and coincidentally occurring more and more when the company is looking to punish a specific talent.
In the case of Mysterio, the company knew of the failure well before Wrestlemania XXVIII (he was tested on February 13th) and continued to attempt to rush him back to work the show. Rey felt he wasn't ready to return in time, however, I'm told company officials made it clear that he was expected to "gut it out" and return in time for Wrestlemania.
The feeling amongst some of the workers is that Mysterio got heat when he told the office he wouldn't be ready to return in time for the pay-per-view. Some conspiracists believe the test failure would have been swept under the rug had he been able to return in time. If true, the credibility of the whole program is suspect as the irony is the "Wellness" policy was used to punish someone who refused to put himself at risk by returning too soon.
As for what caused the positive test, Mysterio is blaming a nasal spray he had been taking that he had a prescription for.