Next, they also need to be drinking. If Someone goes off of feed they are usually not drinking either sure to them not eating if they don't drink and not drinking if they don't eat. If this is the Case you can sweeten up their water by placing apple slices in the water dish, pedialite or Gatorade to keep them hydrated.
In a worst Case scenario, you can boil down old fashioned oatmeal and syringe feed it to them, syringe feed oxbow critical care or just water to attempt to get them back up and eating.
It can take hours, days or weeks to get them to eat regularly again but with time and patience they eventually will come around.