Prompt: Draw an exhausted pony/Draw a pony burning out.

Ha, in my 'verses, there's this thing called Burnout, which is when one pushes their magic to the limit and consumes all of their arcane energy. This is incredibly hard for earth ponies to do, slightly easier for pegasi, and relatively easier for unicorns. Alicorns? Well, depends on what they were doing, but their energy pool is significantly higher. In the Wheelverse, alicorns are usually also deities so it's almost impossible to exhaust themselves in that way but. shrugs
Most ponies, once Burnout has been reached, are unable to cast any spells or channel any sort of magic until their arcane energy replenishes.

However, some ponies can push past Burnout, and the energy for their magic is drawn from their physical energy instead — which can be very dangerous. Sugar is normally the first thing to be administered — to help replenish the used energy, along with bed-rest and then some more food. However, if you are aware that you might need to push past Burnout, scoffing a large amount of high-calorie food before and during the post-Burnout stress is a common tactic and can actually have some beneficial effects on your magic — it might even extend your pool out a little longer.
Rarity, for instance, actually uses post-Burnout energy drain to keep herself in shape after her ice-cream binges while she makes dresses, which is why she's telling Rainbow and Pinkie to find sugar for Twilight. Starlight's had Burnout a few times but never pushed past it.

Twilight, though, hasn't quite had the experience of post-Burnout too often — her pool was so abnormally high in the first place she rarely approached her limit even while she was just a unicorn.

The others are all understandably concerned.

Oh! And this is Starlight's first appearance — her Real Horse Marking is a bald face blaze.