Yeah, that sounds like depression. Hate to break it to you, but yeah. Depression is fairly misunderstood, and most people think it's just being sad all the time, but it's primarily just lack of feeling about anything. It's probably a chemical thing, like Silverblade said, and while it sucks, you can get over it. However, you probably won't be able to get over it just by trying to fake happiness if it is depression. You basically have to reset your system, in a sense. It's not like brief anger (road rage) or a phobia. Talking through it can help, but no amount of cat videos will magically fix your ennui. Good luck.