Hi and welcome to the Chiari forum,
Chiari symptoms cycle, so they can come and go, change in severity....for no reason or something could trigger a flare....sometimes we continue to have symptoms, but we are so use to them we do not notice until they flare.....
You may have increased ICP or developed POTS....or a syrinx....it can change...when was your last MRI?
Hello. I can certainly sympathize with your battle with vertigo. Living with this affects so many areas of our lives. My challenges with vertigo are pretty bothersome, so I have have concentrated on a few specific changes. You should find whatever makes your stomach feel better with your nausea. (I have found that ginger candy works well).You did not mention nausea, but many times the two occur together. Another key change is that I consistently hold onto railings when I use stairs. No more running up and down. Try to always keep your head up when you must bend over - bend your knees rather than bending from the waist. Another thing is to avoid turning your head to either talk with other passengers or look at beautiful scenery when you are a passenger in a car. That is my big issue.
I am not sure I know the reasons for vertigo while lying down. Do you sleep on your back? If so, try to turn on your side and maybe put a pillow between your knees. I hope you can find some relief. Vertigo is tough to deal with.
Vertigo can strike if we are prone or upright....and it does not matter if you are on your back ,side...if you move, it gets worse....I use to get back episodes and it felt like my bed was spinning so fast I would fly off....lol....so glad that is behind me now....but as I said can happen regardless of your position.