The first thing I notice when heading for a deep depression is lack of appetite. I feel hungry, try to eat, but can't swallow anything and gag. If you can get anything down, try pudding, applesauce, things that don't require chewing and slide down easily (Ensure or other nutrition drinks too). You won't starve or cause damage if you can only eat a small amount for a time. But do get to doctor if you can't eat at all.