@Conred
 
One, that’s an out of universe problem.  
Two, as Fluttershy says, he likes using his powers to create problems, but he doesn’t like using them to fix problems, including the problems he creates. The latter part in particular is what makes being around him so intolerable, especially since so many times the problems he creates are the ones that involve people potentially getting eaten by giant monsters.

To be honest, Discord using his powers for good would make Mane6 not important since he could always replace them when a new threat appear.

@PonyPon  
Because it frustrates you in-show.

@Millennial Dan  
Thin air? flew too high?  
It1s cheap yea :p

@anonymous-pony  
It’s not like she had a choice, and the altitude doesn’t look like anything she’s not used to.
 
@Miss Shy  
We’ll stick with that for now.

Ok, so my theory is that the other time period atmosphere is different and unfamiliar to Fluttershy, so she passes out due to being in too much pressure.

@Millennial Dan  
Put it like this, if you were flying at an altitude of god-knows-how-high, at speeds that were close to breaking the sound barrier and having an argument, you’d find yourself becoming well acquainted with the ground before you’d save anyone. Why, because of stress.
 
When you’re stressed and you’re pressured to do something, you end up doing yourself a disservice, let alone the life you’re trying to save. This is just the consequences of fighting while exerting yourself to physical extremes.

@PonyPon  
Realistic or not (and I really disagree there), it’s totally inconsistent if that’s what they’re going to claim. It can’t be something that out of the blue, I would hope.

@Millennial Dan  
I know, this is more realistic.
 
As per my comment earlier, this is usually about the time her ultra mode would kick in and befuddle everyone in its unstoppable badassery.

@PonyPon  
It has to be something else, that’d be way too cheap. Not a single time anywhere in the show has that ever happened.

@Millennial Dan  
Overexerted herself.

What the heck happened to her?

This is something that pops up in the show a lot, and I think it’s a really cool concept. Discord is honestly trying his level best to be a good friend, but at the same time he just straight up cannot understand how to be anything but a manipulative trickster. He’s trying to filter this ‘frendship’ thing through something he knows, but the only things he knows are mischief and chaos.

THANK YOU Fluttershy.

Why does this comic always want to meta about things that frustrate me in-show otherwise?
 
And where’s your Mama Bear Speed Buff now, Shy?!

How about catching her with your limitless magic? Huh?

Wow. Burn.