incircles,

From your description, it sounds like you brought on a decompensation. Most likely from when you held your breath. You PCS brain has much less tolerance for low oxygen levels. You may have also aggravated your brain by straining and raising you blood pressure. The strain can cause the blood to not drain from your brain properly, thus depleting oxygen and increasing Intra Cranial Pressure. Both are not good for a PCS brain.

I can not hang upside down or do a head stand. Even leaning over to reach into a chest freezer or engine compartment can mess me up. So, if it makes you feel bad, do not do it. It might take a long time (year or two) to heal enough to be able to put these stresses on your brain.