Do you derive the same benefits of sleep while just lying still?

Not quite the same as sleep. Apparently here is a bit (to use a computer analogy) of a reboot going on in the brain and in the body itself during sleep. Restorative hormone changes, a bit of helpful blood pressure and heart rate changes, all that are done during sleep that does not happen to the same extent with quiet time.

Yet meditation gives one much of the same benefit, just not to the same extent.

No. It all has to do with brainwaves. Not the same.

My Mom used to tell me it was the same when I couldn’t sleep. (Not sure if that was to get me to relax orto get me to go away.) I do think the restful state helps but isn’t quite the same.

Resting is better than nothing, but your body needs REM sleep, from what I understand.

Sometimes what happens with me is I wake up early in the morning and lie awake for about 3 hours, until the time I’m supposed to get up. At that time, I’m very rested and then will fall back asleep for an hour. When I wake up from that, I’m groggy and usually running late but I feel like I needed that extra hour. The sleep is totally different than the hours of lying in the dark.

No, your body needs REM sleep.

All your body needs is physical rest. As far as your body is concerned, lying still in bed for eight hours is just as good as eight hours of sleep. Sleep, however, is used in order to recharge the brain. It turns out that the brain uses so many resources that it tries to cut corners whenever possible. This means that the same machinery used for thinking is also used for repair. In order for repair to occur, the brain must be in a sleep state. Likewise, it is currently believed that the function of dreams is to help integrate new information into a more permanent form of memory storage; people who have brain damage interfering in the ability to dream lose the ability to learn new skills.

So in the short term, rest is perfectly adequate. Over the longer term, sleep is necessary for proper functioning of the brain. If you can’t get sleep, rest is second-best, but eventually your brain will begin malfunctioning if you don’t get sleep, eventually becoming so dysfunctional that autonomic processes like breathing and hormonal balance will fail and you will die.

Yep, for full rejuvination you need REM sleep. This is why I have never been a napper, I just wake up feeling worse because you cannot attain deep, restful sleep in an hour. Unless I am sick I never nap, just go to bed early.