The extreme cold and extreme heat affects everybody, but even more so with people who suffer from depression and/or anxiety disorders. I have anxiety and I do find this heat makes it worse. I don't feel well, I feel very drained and can't motivate myself to do much.
When I start feeling that way I just MAKE myself DO something. Whether it be cleaning up or laundry, watching TV or talking on the phone, or posting about
how I feel - It helps. Distraction is a huge plus!!
Do some meditation and positive thinking. It works and is good for the mind, keeps you thinking better thoughts.
I get SAD in the winter, not in the summer. I know how crappy you feel.
Hang in there! It will get better.