it depends - if a person is depressed they tend to sleep a lot - it's a form of escapism. Similarly, if you exercise heavily (say with weights), then you'll tend to sleep more on the day you exercise - this is normal, your body is just recovering from it's stresses.

Normal time is 6 to 8 hours - as a general rule, it's not healthy to fall below six (you'll steadily lose muscle mass over three months of this) and it's not healthy to go much above ten (your whole mind and body will become sluggish, it might even lead to depression)