The key statement for me in the original post is the vertigo mention. I don't see bad air being a cause. Some people do get queasy without a visual reference. Low vis after being used to diving in unlimited vis is highly likely to be a trigger. Without a visual and perhaps tactile reference there is the possibility of mild disorientation that will lead to nausea.
Fortunately there are several easy solutions. Number one of course is to use proper buddy skills so that your buddy can be used as a reference. Visually and for touch contact. When you start to feel this stop swimming, look at your buddy who should be within arms reach right next to you, if they are not then get in that position, and reach over and grab their elbow. Don't just touch them. Grabbing the elbow actually will give you a greater sense of stability.
Another is to create your own reference with a float, lift bag, or DSMB and a reel or spool. Having this visual and tactile reference will allow you to be in contact with something that also provides the sense of being stable. Knot or mark the line to show different depths for an added measure of security.
Lastly if you know where the bottom is and how deep it is, get close to it. Not actually on it unless you're feeling really squirrely . Once you have a visual reference the feeling is likely to dissipate. If there is a large rock, log, branch, or other item that you will not damage by touching it, reach out and rest a finger on it.
At this point it may not be a bad idea to perform some task to focus on such as shooting a bag, taking a photo, or making a sketch in your wet notes or on a slate. The idea is to bring the mind back into control.
