It is a Dracaena marginata. Probably wet feet and due to overwatering and insufficient drainage.
The underneat pots only "look nice" and "protect furniture" they don't do a whole lot of good for the plant if it then sits in a puddle.
The soil may have soured but that perhaps is a job for spring.
In the meantime I'd put the pot somewhere it can drain .out fully so at least the surface soil becomes dry. Find some large stones/bottle tops or anything else that you can place in the bottom of the saucer so when you return the pot, it is up a little. Drain off extra water don't let it sit there.
Even if the stem lost its leaves, if it is still firm not mushy it might be broken up and potted to try to strike more plants.