I applaud anyone who went down the upper deck slide! Unless you have stood at the top of one and seen how high it is- it is seriously high and steep- you have no idea!
Asking as SLF here -- I've read that broken/twisted ankles can happen easily when using emergency chutes. I recall that they used to ask pax who reached the ground early to help slow others to avoid further problems. Perhaps I'm too oblivious to the safety lecture these days, but I don't remember hearing that for a while.
Running in terror versus being a brave hero helping others is always a chance event, depending on the situation.
My husband is afraid of heights, and might be seized by fear when faced with sliding from the upper deck if given a chance to think about it. (No offense intended to him -- he's fine normally and has no fear of flying.)
What do you do if someone gets paralyzed with fear? Shove them? Rush them out so fast they have no chance to think? Say reassuring words and pretend it's a playground slide?
I recall from safety briefings that you're supposed to kick off your shoes first. Is this to keep them from catching and spinning you around, or, if wearing heels, to avoid gouging (and perhaps deflating) the slide?
If ever faced with sliding down an emergency exit, I hope I would treat it like a fun ride in an amusement park, and let fear kick in later.