Not only is the overall atmosphere and art direction here absolutely fantastic, but I love what a relatable mystery this animation presents. Like, neither the audience nor the subject know what exactly is happening to the subject inside OR out, and while there are more questions presented than answers as the animation continues, you can still relate despite the entire situation being unfamiliar because it's a universal human experience to go through an unfamiliar situation where you aren't sure what's happening and you can't tell how to feel about it as a result.
That said, TL;DR: the overall uncertainty and unfamiliar relatability of the plot here combined with the tone and atmosphere of the in-story world make for a really creepy and unsettling piece that leaves me wondering more despite having concluded in a satisfying way. 10/10 amazing work!! :D