Are your temps round 24°c?
Best thing to do to address all the issues brought up that it could likely be would be to first check the roots. Gently separate the soil from the edge of the pot by giving a squeeze all round. Then gently turn the pot upside down holding the base of the stalk. the pot shout come away easily. Inspect the roots for anything other than white or off white, if you see dark grey or brown roots then it is indeed a root problem. If not stick it back in the pot, and flush. Bes way to flush is to take it to the bathroom, and poor slowly three times the volume of the pot in water thru it, you really should use pH'd water for this. After you have done this allow the soil to dry till about two inces deep is less than moist then feed with 1/4 strength nutes. Slowly increase the nute ratio over the next few weeks.
It shouldn't take to long for the little thing to perk up if it does then there is another under lying problem.