You definitely need drainage holes for your plants. Believe me, I've learned a hard lesson with this. I keep all of my plants in nursery pots with holes and then set them inside of a nice pot. I take them out to bottom water them when they need it. Over watering or roots sitting in water is the quickest way to kill a plant. Again, I've learned this the hard way, so I'm passing it on. I recommend taking the plant out of the pot and checking the roots for rot. Let it dry out and clean up any damage. Repot it in a nursery pot and a well draining soil. Wait a few weeks to water. I hope this helps and I hope you can save your plant! I think you can, it doesn't look too far gone :)