Why is it that I don't want to do the things I used to love doing?

I have been suffering with depression and suicidal thoughts for a long time now. I just don't understand why I don't want to do the things I love anymore. I used to really love horse riding and playing badminton, being with my friends and going out to the pub. Now I find it hard to even get up out of bed because I know I have to face the day. I don't want to be around my friends anymore, I just don't get it.