If you are feeling down, the best and quickest way to pick yourself up is to help someone else.
When you are in a funk, the focus is on you ... what's going on, what you have done wrong, what someone has done to wrong you, .... Helping someone else takes the focus off of you and puts it on someone else. You get a break from your own drama. You are thinking about and working with another person, which will give you a much needed break from your problems.
Plus, helping someone else gives you the ability to make a difference and get the kind of closure and completeness that might be lacking in your own situation. While I was unemployed and in danger of losing my home, I volunteered. Helping people write a resume or solve a problem was empowering. It gave me the opportunity to do something, something that yielded real and tangible results for the other person. It gave me a welcome respite from my own problems.
Finally, those people I helped were grateful and appreciative for the help I was able to give. The gratitude felt good! And I needed it! In helping someone else, I was able to help myself. Talk about a win-win!