bad dream or a nightmare
http://www.youtube.com/user/iamxiaoli has a Halloween themed lesson where she says, 我昨晚做了一个噩梦。 I find two ways to write nightmare in the dictionary. 噩梦，恶梦，词典告诉都一样。朋友说恶梦=bad dream,噩梦=nightmare.
Is there a difference between 恶梦 and 噩梦 however subtle?

Question

bad dream or a nightmare
http://www.youtube.com/user/iamxiaoli has a Halloween themed lesson where she says, 我昨晚做了一个噩梦。 I find two ways to write nightmare in the dictionary. 噩梦，恶梦，词典告诉都一样。朋友说恶梦=bad dream,噩梦=nightmare. 
Is there a difference between 恶梦 and 噩梦 however subtle?

Answer

No difference in my mind, but I like "噩" to express nightmare. The symbol itself just makes you feel more terrified compared to "恶". Historians might track into ancient literature to give you different answer.

Answer

your friend is right.

Answer

I think Chinese people don't differentiate these two words, at least not in daily conversation.

Answer

hello, 噩梦=恶梦。but most of the time ,we also use “恶梦”. because噩梦 is like  an ancient Chinese words，it write with intricate. now replace the 噩梦 with 恶梦.

Answer

if you can define the diffferences between 
nightmare and bad dream. you'll get the anwered.

yeah, they are similar, but not exactely