Beginner Gardening: Ailing calathea, 1 by ataraxia

ataraxia wrote:
This poor guy, after losing most of his leaves (long story short, I let his roots stay too wet for too long before switching to a faster-draining mix) was hanging on pretty well for a couple of months with just the 2 leaves. A few days ago, they sort of folded in half and stayed like that. Its environment hasn't changed (it's in a terrarium/greenhouse with several other calathea varieties, which seem to be doing fine). Could it be heat stress (it does get a little warm in there if I don't air it out every day)?