Uncomfortable chairs are a problem for me as well. They can cause a back pain flare, driving does this after about 15 minutes, or hard chairs cause a muscle spasm in very uncomfortable areas ( pudendal neuralgia ). I have Valium for the latter, probably not an option at work, and take ibuprofen for the back pain.
There is probably a relationship between the stress of the meeting and the effects of the chair- imperceptible muscle tension really escalates the way pain winds up.

Everyone says to avoid stress with chronic health problems, but that seems impossible in real life. Hope you are back to feeling better.