What are the "lower levels of consciousness"?

What are the "lower levels of consciousness"?

Les Weiner (Former Chair of the Department of Neurology, University of Southern California) gives expert video advice on: How long can a person be in a coma?; What is "persistent vegetative state"? and more...

There are different kinds of levels of consciousness. So you can be sleepy. You can be lethargic, which would make you less lively. There's stupor, which means that you are essentially non-responsive. You can make sounds and moan, but you're not going to say anything. Then finally, you are in coma, where you are not arousable. These are all lower levels of consciousness.