Avocado pits are often sprouted in water, that may explain why it was in water when you got it, if that's what it is. In insufficient light, the growth may be artificially stretched out, if that's a factor, which it probably is if that's where the plant lives, by the stairs. That can make it a little harder to ID, comparing to pics of healthy specimens. So... it was in water for years until how long ago? It's not unusual for any plant making such a transition to lose some leaves. Soggy/mucky soil would be more harmful than helpful although it seems counter-intuitive to suddenly put it in much more dry "soil" doesn't it? If there isn't some sun shining directly on it for some part of the day, that's probably not enough. If it is an avocado, those grow in southern FL and Mexico with no shade. If you think it needs more light, take it slow, like an hour or so the first week. Not sure it matters though, looks like most of the leaves are dying and new growth could pop out pretty fast, which would not be at all sensitive to sun like the older, used-to-being-inside leaves.

Though I can't say what variety it is, but it does look like the typical succulent house plants that do not need too much water. Your last pic shows a very good soaking which is good for other plants, but may affect this one negatively. Anyway, it's good to learn about, but try to stay on top of it and if it looks in bad health again, just reduce some of the watering. It looks like the office mascot by this time. I do want to comment that until you could properly identify it, it looks like it may be leggy either because of lack of proper lighting before, or it might be one of those plants that "trails", so if it starts toppling over again, that might just be its attempt to be more horizontal than vertical, and not necessarily because of lack of water. I mention this because while in the original pic, it was being more horizontal (for which we don't know the exact reason yet), but in the second pic, you have planted it as a more vertical. It could be that it is a trailing plant.

Looks like H. rosa-sinensis, as several have stated. I don't see your location, but if you are in a cold-winter locale, you can probably maintain it indoors over winter. Give it as much sun as possible. Keep it evenly moist...never sitting in water, never bone dry. It will lose most leaves up to the tips due to lack of humidity, and watch for mites, too. Since it's a woody perennial, it will hang in there until spring, but look pretty bare. Once spring weather is settled and regularly above 50, it can go out on a deck or porch, gradually getting it used to full sun. Fertilize it regularly and keep it watered and grow it hard and fast to get buds and blooms before cold weather sets in again. I'm in Indiana and repeat that cycle annually for about ten big pots. Boy, do the leaves drop when they come inside! It is not a houseplant and will struggle if it's inside all year, though you may get a few blooms. Good luck with your plant. I love the tropicals and don't mind the work. Bob

Yes indeed. Thank you very much for helping to identify my plant. I really appreciate it.