I really advise you to read the ebook from the link I gave on my last post, if nightmares, bad visions and bad signs are something regular on your practice.
You will understand that they are just the reflex of bad karma - probably from previous lives - and also that they are just samsaras. Ignore the bad omens that you may find on your practice. Focus on what you have to do: nembutsu. Sensations are just sensations, be it good or bad, and a vision wont be a threat.
But if the bad visions you have are not during your practice, but while dreaming, it seems that you need much more practice. Who knows, only within years your bad dreams may stop. There are many factors here: heavy/bad karma from previous lives will affect your dreams, but also your current personality, your brain structure itself, what you do during the day, what you eat before sleep, etc. Finding the solution is hard.
I have bad dreams many times too and since young I have lots of trouble sleeping. There are some things that may help. One of them is physical exercise. I dont have a lot of time to do it (as a teacher, I must prepare classes for the next day when at home (at evening/night) and be in the school during the day, so I dont have any time for exercises, but when I do it, I will feel a LOT better and sleep much more.
I am to much of a thinker guy in a "thinking" job (I mean, a lot of bureaucracy & lot of stress dealing with classes), so the exercise is very important to me. Try that, it may help you too.
I read the link you provided but the teacher describes one experiencing evil hell realms. I don't I've ever experienced such a thing in my nightmares. I believe my nightmares are more related to my bad thoughts, deeds, and memories in this present life.