Read some more on the Smash Mouth situation.
Turns out Steve suffers from Wernicke’s encephalopathy. Which explains a lot.
For those without any knowledge of the brain, it’s a particular form of brain damage where lesions form on various parts of the brain. The lesions are chemical in nature, formed from B1 deficiencies (Steve has a bad heart condition too, and his medication likely made that worse). He has also struggled with substance abuse, including alcohol. If his addiction was bad enough his illness may have progressed into Wernicke–Korsakoff syndrome, basically a fundamental collapse of the brain’s structure due to lesioning and atrophy. Heavy alcohol consumption further depletes the body’s levels of thiamine, which leads to more lesions. Alcoholics also tend to not have the best diet, and the brain damage will lead them to make worsening choices, see the cycle forming?
Anyway, it can lead to severe memory loss, disassociation, loss of emotional control, loss of motor function, I mean really any nervous problem you can think of since the lesions appear all over the brain.
So he was likely having an episode on stage.