Twilight writes her report (Patreon)

Twilight's quill danced across the paper as she composed her letter.

 Dear Princess Celestia. As promised I am keeping you abreast of Spike's  condition here in Ponyville. After further tests and observations I am  of the opinion that he is not suffer from another bout of Dragon Greed.

     Instead I am labeling his current condition as Uncontrolled Draconic  Drooling, or UDD. At first I was baffled by his symptoms since they  didn't match anything I have been able to find in tomes related to  Draconic health. It does not appear to be caused by any virus, bacteria,  or allergic reaction. However along with his drooling, Spike has had  bouts of incoherent speech, heighten pulse, breathing, and blood  pressure. Also the bouts seem to result in what can only be described as  a carbonating of his hormones.

    However yesterday I had to  drop by Carousel Boutique to pick up my ball dress. Of course Spike was  with me and upon entering Rarity's establishment the young dragon had  another episode when she came out in her new work uniform  .  I quickly took the poor fellow home and put him to bed. Then later  afternoon Pinkie Pie dropped by. 

      She'd heard that poor Spike had another  attack and she wanted to cheer him up. However upon her entering his  room the poor little dragon had another bout of UDD.

    At that point I realized that Pinkie was also wearing a variant of Rarity's work uniform. She'd recently purchased it to help Rarity out at her boutique on days when she's not needed at Sugar Cube Corner.

     I believe it's these outfits that is triggering some pre-conditioned  response in Spike. To test this theory I've asked Rarity to quickly put  together a similar outfit for me. I will wear this outfit when I take  Spike his dinner and see if he has a similar reaction. From there I  maybe able to develop a treatment for the poor little guy. I will keep  you abreast of further developments.

Your friend
Twilight Sparkle