It may have been getting too much water. How often do you water? What is the soil mix it is in? Please post a picture of the soil mix.

Have you checked for mites? Do you know how? How do you know how to spot them? Is your mix compacted? Does it drain too fast? Does it get evenly moist? Do you water in sips? How long does it take for you to water the next time? Are you sure your mix is getting thoroughly wet? Is it in peat moss? Do you flush you mix out once a month? Have you you forgotten to water recently and saw the leaves wilt? Have the leaves ever wilted from thirst?

A lack of sunlight will not do that...if kept too warm and a lack of sunlight, the leaves will just fall off. Spider mites will also drain your leaves of moisture and rob them of their vitality while still clinging on like that.

If your roots were happy and you kept that room cool with at least 4 hours of sunlight or less, it would still stay green but not produce as much blossoms if any at all..