What's the difference between nightmare and dream? Based on Wordweb dictionary,
Dream is a series of mental images and emotions occurring during sleep and dream is an experience while sleeping.
Nightmare is a situation resembling a terrifying dream
So NIGHTMARE is considered DREAM but it's a bad and terrifying DREAM

I hate having nightmares. I've been getting nightmares for the past few days.
I'm kinda afraid to sleep tonight because i don't want to get another nightmare.
Oh in my dreams, i was attending somebody's funeral
but i didn't know who that person was. I didn't even know where i was.

I swear it was really scary. I saw a dead body wrapped with white cloth
and the body was placed in the living room where people gather around it and pray (just like a typical malay funeral). That's all i could remember.
Thank god mum woke me up so that i won't have to continue with the nightmare.
I hope i won't get another nightmare tonight.