I get something called closed eye visuals sometimes. It is like closing your eyes and watching your subconscious to a certain extent. I've also lucid dreamt and that is like seeing those images in a 3d space. Closed eye visuals can be like 3d, but mostly for me it is like a projection behind my eyes.
Anyways, some of us may think in images, or a more correct way to say this might be, is that we have an occipital lobe which is dedicated to processing images.
Have you considered that waking to images, is really nothing more than catching a glimpse of your subconcious thoughts, right before you wake?
Understanding the subconcious language of the mind could be something entirely different however. For example, why did you feel it was okay to relieve yourself? Here, this might be something you are interested in trying.
https://www.youtube.com/watch?v=W96a_WAQeNk
Anyways, there are other mechanics to the mind, melatonin might regulate your sleep, um, acetylcholine or nicotinic receptors might somehow play a role in the crispness or resolution of your subconscious imaging. All the details are probably known to a few select dream researchers, I just don't know the specifics. Maybe the chemistry in your brain was off in a way where urinating became top priority to get fluids out of your system so your bladder would have more room for filtration, in order to rebalance your blood and brain chemistry through the kidneys? So, any minor chemical imbalance gave you a quick glimpse into your subconscious processes? I don't know.