Indoor plants can suffer from a bevy of environmental stresses that results in wilting stems and foliage. Wilt is a fairly rapid response signal that something is amiss in the plants' immediate environment. When caught early wilt can usually be reversed by correcting the underlying problem and preventing its recurrence.
Too Little Water
Most indoor plants suffering drought stress will respond quickly by wilting. Drought stress can occur from chronic underwatering, a periodic lull in watering, which often occurs when on vacation. It can also occur when a plant is so rootbound in the container that there is too little soil to hold moisture to the roots for the plant to absorb. Underwatering can also be exacerbated by poor quality soil that has been stripped of all organic content and cannot absorb water any longer.
Overwatering & Root Rot
Indoor plants often suffer from over-watering. Indoor plants do not typically consume as much moisture as the same plant would planted outdoors in the garden soil. When grown in containers with limited or no drainage holes or when plants are allowed to sit in saucers of water over time the roots suffocate and rot. All of these will cause the plant tissue to wilt and sag and may even discolor them turning pale green or yellow.
Fertilizer Salt Build-Up In Soil
Commercial fertilizers contain mineral salts. Since the soil in container grown indoor plants is trapped and does not always get watered sufficiently to leach the salts out of the soil, plants can suffer from the build-up. The salt impedes water uptake, which can cause wilt or can become toxic, which can also cause wilt.