You feel horrible because you ran out of antidepressants. This is why you have a) no motivation, b) a headache, c) a nagging sense of d00m. You went to the pharmacy and have some more now. Nothing is actually wrong except for the running out of antidepressants (which was not your fault anyway, you put the repeat prescription in on time, but the prescription processing person didn't read it properly so ordered the wrong drugs), and you have sorted that problem out for now.
Now if only you could believe that nothing is wrong and a) get some dinner inside you so you can b) take the antidepressant.