It would help if you had some pictures of the leaves before they fell
At first they stay green (even the fallen ones). But as the tree keeps declining, some will turn brown along the edges, in an inverted v-shape, starting from the tip.
Temperature stress is something I'll have to look into. Thank you!
It's currently in my bathroom, which is clean but still not very sighty. And I'm currently trying to kinda trellis it as it has become quite unwieldy and I can't really move it much without risking it.
But I'm planning to relocate it after pruning next spring. As soon as the leaves have grown back, there will definitely be pictures! :D