First of all, I think that you'd have little to fear in regards to encountering that nightmare entity. The dreamspace and hyperspace seem to be worlds apart, having little to do with each other. In regards to the breakthrough, I would also advise that you start low and work your way up. The thing is that many want to rush and jump straight to the breakthrough (I was the same), but those who do manage to achieve a breakthrough right off the bat can tend to be ill-equipped for handling it. In the absence of lesser experiences in which the user could have become acquainted with what goes on in hyperspace and consequently how there's little to fear, premature breakthroughs (breakthroughs most likely being the most intense experiences a person can or will ever have while still alive in this dimension) can instill a great amount of fear in those unprepared causing them to lock up and start resisting. Resistance is barely effective at the sub-breakthrough level, and if you're having a breakthrough experience, you might as well be trying to use your mental powers to derail an oncoming train. The key to all these experiences (and especially the breakthrough) is passive observation and letting go. Any attempts to try and control or resist will usually only result in further frustration and trauma.
It's easy to read these words and try and keep them in mind, but if you have a breakthrough bulldozing through your door and you're not ready, then you'll have wished that you would have had less intense experiences (also which may easily be the most intense experiences of a person's life) to get accustomed to hyperspace and to disarm some defensive, self-destructive psychological reactions that some seem to have a harder time than others in dealing with. Part of what I had to learn first hand was that no matter how scary or dark or intense an experience gets, if I have the patience to sit back and just let DMT run its course, that there's usually bliss, love and light waiting in the wings. Bearing this in mind, there have been significantly few experiences that have been even remotely scary or freightening despite the sheer intensity and absurdity of some of the realms I've frequented.
"Science without religion is lame. Religion without science is blind" - Albert Einstein
"The Mighty One appears, the horizon shines. Atum appears on the smell of his censing, the Sunshine- god has risen in the sky, the Mansion of the pyramidion is in joy and all its inmates are assembled, a voice calls out within the shrine, shouting reverberates around the Netherworld." - Egyptian Book of the Dead
"Man fears time, but time fears the Pyramids" - 9th century Arab proverb