Mental. This shit is dangerous though, I'm pretty sure a guy died a couple of years ago doing this (flew into a bridge?).
Jeb Corliss is another guy who is pretty famous for flying in those wing suits. I'm pretty sure recently, when doing a low pass (like near the balloons in this video) he clipped the rocks with his foot or leg and took a spill.
This is very extreme, and you gotta have a lot of experience and guts. Scary, 1 wrong move can mean death.
These videos just prove there is NOTHING that should stop you from your goals. NOTHING is impossible.
I am so much more comfortable thinking about doing this than pure skydiving. To me, skydivers are the ballsy ones.
What would these daredevils do next? Throw the parachute first and dive after it 5 minutes later? WOW! Do those guys ever watch their stunt videos? They'd be sh1t scared simply watching it as a 'third person'...