Why would anyone draw their own nightmare? 
nightmare; a dream that results in feelings of extreme fear, horror, distress, or anxiety.

for me, when a friend talked about herself having constant nightmares, i thought she should express them out.
since she's good at drawing, she can pour her nightmare out into drawing.
i cant draw, i write. so, i pour it out into one document and save it on my drive. express and lock it away.

speaking of nightmare, who never had nightmare before? everyone did. everyone still does. the unpleasant dream that is succumbed from a problem we suppress into subconsciousness. any dream will show you what your mind have been holding of lately.

i hardly talk about me having nightmare, as i said above, i write. at least, i express them, i confront them. and im on the way of healing myself.
because, instead of letting someone else, pointing out 'what the problem is' by myself is much better.

confront your nightmare, talk to them, soothe them like you would to a wounded friend, and watch them dissolve. 

i find some inktober vids (related to dark things, nightmare) on youtube. if i could draw, i would go for this vibe. lemme share it below.
one,
two.
Oh, and I just found this video, if you can't draw, having an illustrator is also an option for you to express your nightmare: three.