Is it a Sleeping disorder..?

Okay so my mom sleeps a lot! Like no joke probaly 16 hours a day. And she doesn't just sleep to sleep she's accualy tired. And she doesn't do much. All she does is go to work and I know that's not that tiering. Does she maybe have a sleeping disorder? She went to the doctors and they took blood test and said everything is fine but I was thinking maybe its a mental madder. Is their something wrong with her? If so what? Please help.