Sleep is actually a complicated issue.
How well a person functions not only depends on how much sleep they get but also on the quality of sleep they get. True restorative sleep only occurs during REM sleep. A person can actually sleep 10 hours straight but if they never reach REM or do not reach it enough they are going to feel like they barely had any sleep at all.
Some researchers also theorize that when you wake up plays a part in how restful you feel. They think that when you sleep your body recharges in a 2 step forward 1 step back way and that the 2 step forward part is sort of stored temporarily until a full cycle of REM/Non Rem sleep is finished and then part of the stored "energy" is transferred into your usable "battery" and the rest is dumped. They also think that if you are woken in the middle of a cycle all that temp energy gets dumped and is wasted. In conjunction with this theory some researchers think that a person can only get so many hours of sleep per day and that if they go over that then everything they accumulated gets dumped and the body starts all over which would account why so many people who end up sleeping a lot more than they usually do end up feeling more tired.
On top of all that everyone has a "Sleep Bank". Just like a real bank you make credits (restorative sleep) and withdrawals (when awake), and just like a real bank account when your account is doing well you have few worries but when your account gets low you start to have issues. When your account gets too low a little extra sleep, beyond what you need for the next day, can help build up credits in your sleep account which can help you get along better during those times when sleep time must be shortened. In a way it is like taking out a loan, even though it is from your own account. Like any kind of money loan though there is a type of interest payment that has to be made so if you borrow an extra hour from your account it will take more than an extra hour of sleep to make it up. Some researchers though believe this sleep loan is more like a "payday" loan than a regular loan where the interest rate is very high, like 2 to 1 or 3 to 1. Some also theorize that there is a limit as to how much you can "re-pay" at any one time.
That is only the broad strokes of the picture, and everything plays into everything else.
If a person is not getting the amount of restorative sleep they need regularly then the occasional extra long sleep is a good thing, but if someone is sleeping excessively quite often then they really are doing themselves more harm than good. Sleep like everything else is great in the proper amount but too much of it is not good.
The real question is how much sleep is good and how much is too much. To a great extent this is a very individual answer. The average adult, who is not ill or injured, requires between 7 and 10 hours per night. Some people though may only need as little as 5 or 6 or as much as 12, but it is generally agreed upon anything less than about 6 hours or more than 12 is not good for you if this is what you are getting on a regular basis.
2 confirmed herniated lumbar discs. Spinal Arthritis. Spinal Stenosis, diabetic peripheral nueropathy.