The hardest one to spot
Answer in your head first.
Someone says: I am not depressed, I have just become lazy and ungrateful and I need to pull myself together. Why is that sentence worth a second look?
Because self loathing is one of the symptoms, and it does not arrive labelled as a symptom. It arrives in the first person, sounding like an honest assessment. Losing the ability to do what you were doing three months ago is a change, and changes have causes. Laziness is not a change, it is a verdict, and it explains nothing.