I used to sleep 12-14 a day; it was getting really bad. I was always tired too so it's not like it fixed anything (I also used to fall asleep anywhere and everywhere). Now I get 4 hours of sleep (there's not enough time to do everything in a day) but I do try to aim for 9 hours. The 'healthy/normal' amount of sleep is ~8 hours though.

The reason you may be oversleeping may be because of your mental health (not too sure about meds and their affect on sleep) or a health issue (e.g. thyroid or anemia). This is what my aunt said (who is a family doctor) when my mum complained to her about me sleeping too much.