I don't think anyone has a life that is constantly happy. Some people just have the temperament to handle things differently. It doesn't mean that everything is ok in their lives and it doesn't hurt them. Some of us just get to have the hardship of showing more emotion than others. Some of us can't hide it like others can.

If someone seems to be perfectly fine all the time and upbeat constantly, either they are really trying really really hard to be that way, or have been through a crisis that makes them value life no matter what happens, or they should be "evaluated" lol.

If you don't feel like leaving the house, do the opposite. Get yourself out when you are in the slump. Do the opposite of what you feel....it will probably help you out a lot.