I've done a fair bit of research on Depression for personal reasons, in the past. The major symptoms are loss of interest in pretty much everything - food, family, friends, hobbies, school or work. Pretty much anything that usually gives the person sufficient motivation to get out of bed in the morning, no longer works. The person just sleeps away the days unless forced out of bed.
Someone I am very close to suffered from depression for two years. He wasted away from a big powerful man weighing over 220 pounds to a frail man weighing 135 pounds. He lost all interest in food. He spent most of the time in bed or on the couch. He had physical problems he refused to have treated. It was a nightmare for everyone around him. The upside is that his family finally managed to drag him to a doctor for treatment. A strong anti depressant worked for him, and he finally came out the other side. The thing is, that he has to monitor his own moods. Normal sadness or disappointment can escalate to feeling that nothing at all matters anymore.
Depression is a terrible illness, but it can be treated. There is hope. The first thing toward getting well, is getting help. Your family doctor can prescribe anti depressants if he/she thinks it necessary, or refer you to a therapist if that might help. The thing is, don't give up. Don't ever give up. There are people who love you, even if you don't feel they do anymore.