Ask Mr. Smarty Plants

For general information on this plant, we are quoting from another answer on the same plant:

"The Lemon Cypress is a cultivar called Goldcrest, or Golden Crest, of Cupressus macrocarpa (Monterey cypress). You can read more about the tree from Plants for a Future, Floridata.com and from the Florida Cooperative Extension Service. Here are some intructions for outdoor care from ShootGardening and you can find care instructions for indoor Cupressus macrocarpa at indoor-plant-care.com and from the TopiaryShop."

Just at first glance, the problem you are having sounds like transplant shock. Did you move the plant to a new pot? Was it watered, but with good drainage, on a regular basis? Even if it stayed in the same pot, a sharp change in environment, such as from full sun to shade, or from outside to indoors, can cause transplant shock. For instance, the "mother" plant of this cultivar, Monterey cypress, grows naturally only in a certain part of California, which is pretty different from Collin County, Texas. Or it may have been moved from a regularly-misted greenhouse, to a truck, to a sales floor, to your home, with not much interim care, and be exhausted.

The other alternative, which we hope is not the case, is that it was already diseased when it was purchased or that it has root damage. Sadly, plants are often "forced" into attractive growth or bloom to make them easier to sell, but there is not a sufficient root system to support this growth. This plant is also susceptible to canker that kills the tree, especially if it is grown away from the cool sea breezes. We're going to assume (hope) that it's transplant shock, and try to help you save the plant.

First, no fertilizing. That's usually the first thing people do when a plant is having trouble, douse it with fertilizer. Never fertilize a plant under stress. Next, trim off a lot of the upper part of the plant, 1/2 to 1/3 of the upper structure, only taking care to leave as many leaves as possible, for nutrition. Then, to make sure that there really is moisture around the roots, we like to set the pot in a basin or tub with 2 or 3 inches of water. If your pot has good drainage and good potting soil in it, this will cause water to slowly move upwards in the soil by osmosis. You'll know it's happening because you'll see the water level dropping in the tub. Now, take it out of the tub and let it drain and drain. (Better do this on the porch, all that water might not be good for the floors.) After that initial wetting, try to give it a good dose of water (still making sure it's draining well) every day to every other day. The reason you do the initial soaking of the soil is that water will shoot right through very dry potting soil, and be gone down the drainage hole, leaving the roots thirsty.

Will this save the plant? Sorry, no guarantees, but it's better than watching it droop itself to oblivion.