Get help diagnosing and treating a sick plant. Include pictures, watering schedule, light levels and temperature/location so that we can help figure out what's wrong.
My cousin's dance club cut down this huge piece of their tree and she gave it to me. I immediately planted it into this pot and it even got some new growth super quickly, and, while I was expecting the older leaves to wilt, I didn't expect them to do so only on the sun side.
It is likely that the soil is too dense and retains too much water. I would unpot, remove as much soil from the roots as possible and repot with a soil and substrate that drains faster. Like a cactus mix and some extra perlite mixed in. Then I'd wait a few days for the roots to recover before watering.
How does that explain the asymmetrical drying of the leaves?
Rot does weird things to a plant.
The difference in sun exposure explains that. I second the opinion that your substrate is the problem. Use a gritty mix like the other user suggested, at least 50% drainage. The transition away from peat is going to kill a lot of houseplants!