If you are sick or recovering from sickness (such as the flu) then, no.
However, if you are mostly in good health, yes it is very bad for you. Your body when given too much rest becomes energy unefficient and you have this tired, sluggish feeling. Not excersising can slow down your metabolism and lose your natural ability to fight off illness. Also not standing up and moving around decreases the amount of circulation getting from your heart to your limbs, fingers, toes, and head.
The average person should get 7 hours of sleep and 1-2 hours of rest (not sleeping, but not doing anything physically exhausting) per day.
Sleeping 9-10 hours a day, however, help clear up your skin, if you have acne.
If you are doing this a lot you should talk to your doctor. If there isn't anything physically wrong you may be depressed. If that's the case, talk therapy, and sometimes medication, can help immensly! Please address this issue soon. This behavior can become a habit that is hard to break and hard to take. See your doctor and go from there.