Any studies showing that people have more positive experience after NREM dreams as compared to REM dreams?

[Yusra]

A study in 2016 found that more than half of participants reported having dreams when woken from NREM sleep. While dreams can occur in both NREM and REM sleep, the vivid dreams people tend to remember occur during REM sleep . The study also found that the descriptions of NREM dreams tended to be shorter and less detailed than those of REM dreams

 

[eLdavis]

What's NREM sleep though, I don't understand that part.