I rarely get imagery but one I still remember clearly in the catagory of disturing imagery was of a ladies face, crawling in ants. It wasnt scary thou, just disturbing and in a dark kind of way fascinating.. if I had to choose which imagery to enter into a LD from I would of choosen that one that night, just for the interest of it of why that ant covered face.
Another one which wasnt so disturbing was of a huge maggots face looking at me, half an arm length away from my own face. (its head was far bigger then my own). Those things are sooo ugly, it was repulsive.
The most disturbing dream imagery Ive had would have to be, deformed babies.. babies with broken bones, babies being bent backward so it looks like their backs are about to snap (real cringe material to see).
One can have an incredibly violent dream but it may not be a nightmare. I once due to holding so much inner anger towards my mother dreamed (I wasnt lucid) of murdering her. I bashed and bashed her head against a brick wall, shattering her head and brains, blood going everywhere. Feeling satification at what I was doing. I was only very disturbed by this dream only after I woke up in real life, remembering it in detail (so more of a nightmare only after I woke up!).
I think for something to be called a nightmare..there has to be a lot of fear there and it has to be a dream.. not just an HI. I cant remember the last nightmare I had thou I get a lot of bad dreams. (Ive had two dreams in the past few weeks of a huge tornado forming and being at risk of those.. but they arent bad enough dreams for me to call nightmares. I are scared in those dreams some thou and taking refuge from it).
Nightmare.. a dream in which I will be paralysed in fear, crying in fear, screaming in fear or shaking in fear during it... an intense emotional dream. An uncontrolled LD could easily become a nightmare if a person allowed it to be.
The only thing to fear is the fear itself