What does N1, etc., on hypnogram mean?

I'm wondering what N1, N2, and N3 mean on my Hyponogram. Are they sleep stages?

Yes, they are the sleep stages:

N1 = Non-REM Stage 1, which is tranisitional sleep---what you are in as you are just barely falling asleep

N2 = Non-REM Stage 2, which is light sleep---you are really asleep, but can still be woken rather easily

N3 = Non-REM Stage 3, which is also known as Slow Wave Sleep. This is the restorative sleep you need for your body to repair itself from all the little trials and tribulations it goes through every day.

REM = Rapid Eye Movement sleep, which is very important for your brain. It's when most dreaming is done and it is important in letting the brain consolidate learning and memories among other things. Think of it as restorative sleep for your mind.

Thanks, Robysue.