Deadmau5

During a visit to Six Flags Magic Mountain -- Tommy Lee and a mask-free Deadmau5 strapped on some safety harnesses and swung into action on a ride aptly named "Dive Devil" earlier this month. Safety first.

World renowned DJ Deadmau5 was hospitalized last night after collapsing on stage during a performance at a Washington DC nightclub, TMZ has confirmed. A rep for the Canadian-born DJ -- real name Joel Zimmerman -- tells us he collapsed on stage from exhaustion ... at which point, "medics at the…