PWInsider reports that Jerry Lawler flew to Montreal from working weekend independent in Aruba so he did have a long day of travel before wrestling and working RAW.
A fan at ringside noted that it sounded like Lawler began right before he collapsed. Before that, Lawler communicated with a ringside employee. Lawler grabbed his arm and turned blue as he fell, which could be signs of a heart attack. EMT's and WWE doctors tended to Lawler immediately. His shirt was ripped open so they could begin medical assistance. Lawler was rushed backstage via stretcher and then taken to a local hospital via ambulance.
After Lawler was taken away, the WWE ring crew quickly cleaned up at ringside as it appeared Lawler may have gotten sick before he collapsed.