Even the smallest change can entirely rewrite someone's mindset.

Long suppressed Depression could leave a long impact of a young adult mare, especially one whose been grieving for an entire year, the grieving process of an magically emotional Twilight is complicated.

That was made perfectly clear when the small community of Ponyville is killing each other off, by suicide. The rates of these self caused deaths are enough to raise the red flags of Twilight, but none to the concern of the guards.

Maybe Twilight is as crazy as they say.