For instance a danger in meditation is dullness, which I think I started feeling and found quite scary. My breathing rate dropped to next to nothing a few times and powerful visions and floating sensations. I had to pull myself away thinking I would stop breathing altogether. Culadasa classes this as gross dullness which can be very pleasant, floating, dreamlike but it is in essence a distraction, albeit a highly pleasant one.
Dullness a danger? Crossing a busy intersection while the light is red is dangerous. Dullness is not. Calling dullness a danger strikes me as rather extreme! I would argue that it's certainly something to note and explore; but nothing that need be overly concerning.
It's typical for your breathing rate to drop during meditation. When the breath becomes very subtle and slow that's actually a good sign that you are very relaxed; and if it's accompanied by [hypnagogic] images and unusual sensations that's just an indication that you are on the cusp of sleep (physically), but a bit more aware of this kind of state than normal.
There is no need to pull away from such states. In fact, just the opposite. I would suggest that it would be useful to learn how to navigate your way through these states. You would certainly not stop breathing altogether, as respiration is a function of the autonomous nervous system, over which you have relatively little control.
Culadasa's book is indeed very detailed. He does set out a path, with clear steps and signs of progress. Keep in mind though, that his definition of mindfulness is just one of many, as is JKZ's. I think many people would argue that Culadasa's approach is one in which jhana (concentration) is emphasised over mindfulness.
In other approaches, the very idea of steps and signs of progress is itself questionable; particularly as we are all unique — and many people find they don't fit into such neat little boxes.
For those interested in exploring mindfulness in its many flavours, you may also like to check out When Awareness Becomes Natural: A Guide to Cultivating Mindfulness in Everyday Life by Sayadaw U Tejaniya.
Another recently published book which I found worthwhile is Bill Morgan's The Meditator's Dilemma: An Innovative Approach to Overcoming Obstacles and Revitalizing Your Practice