You need to tip the plant out of the container and get a look at the soil and roots. Is it too wet or too dry? If the roots are mushy and soft you may be over-watering, if the soil starts to crumble on the bottom when you take it out of the container Its too dry.
If its nether, then while you have it out of the container very gently remove the soil without damaging the roots and replace with fresh new potting soil . Then give it some time to recover and you should be ok.