Ginger Kat,
I too have unfortunately been in your shoes. You feel like a complete failure. And you have an awful day that makes everything worse and you try to "self-medicate" All you want in that moment is for once second of good feeling. And who can blame you? You have felt like crap all day, and not just today but several days.
So you eat 3 whole things of ice cream,you take your anger out on someone else,you drink or take drugs.
And then when you thought it couldn't feel any worse, it does.
You are left feeling like an even bigger loser.
What helps me know when I feel like you are feeling is to write down one thing I did good today.
Today's good thing I did was get a shower.
It may seem small and unimportant to some but to me it was an accomplishment.
As hard as it you have to forgive yourself and give yourself some slack.

I hope you find some peace.