There are many things you can do to improve your situation. I will not suggest anything specific because you know what you can do, I do not know you. I go through the same thought process of feeling sorry for myself everyday, but over time it has taken up less of my time.
Think about what you can do and use those abilities to better your life and the lives of others. About emotions, you are/control the emotion. It is about recognizing your expressions and moving forward. If you are crying when sad, then thinking about why you are sad will only make you cry more. This applies to when you smile as you feel joy, so that if you think about what made you feel joy, you will prolong the feeling; when you scrunch your eyebrows as you feel anger, and you think about what caused the anger, it will prolong it as well; etc.
When I would get angry, I would then become sad afterwards. I then learned how not to be sad. I let the anger linger in me to think about how stupid it was of me to be angry, or I let myself be angry, but I would not express it violently.
All that I see in your post is thought on what makes you feel despair. Eat, drink something; get some sleep. If you are stubborn about eating, drinking, or sleeping, all it will do is make you feel worse because your body is not just some tool, it is you. Once you get that straight, realize that life is an adventure and you decide what it will be like. If you sit wallowing in despair, then that is what you will have let your life be.
If the world was in ruin left with only me, I will smile at the future, and cry about what I have lost, as I realize what I am without the world, instead of what the world is without me. Become someone who can leave this world with a smile. 