Goodness.. if these are greatly increased upon showering.. is your showering too hot perhaps? I like a hot shower myself.
I had really low pressure post op surgery too, but I lost little blood during the surgery (as it was minimally invasive fusion surgery). They were pretty sure it was the morophine that was mostly the culprit.
It could be your meds, the surgery itself, and also your body is much depleted of many things through this horrible trauma we are in.
For the first time in my life, my blood test showed slight enemia. I was very run down after the surgery for the first several months. I believe this is very normal. An alchemist suggested immediately to get calcium/magnesium supplement to help with the muscles. Miss skeptical me, but in so much pain, went and got some.. and that night I noticed a big difference.
My GP wanted me to take iron supplement and B12. The B12 I take, but the iron.. no way for now! Iron and I don't mix well together. Even small doses gives me all sorts of problems. I feel sick taking it and it also creates severe constipation for me, even with a high fiber diet. I seem to be doing fine and better since taking the Total B line, and will get my blood drawn again in a few months to check the iron level once again. Then if it's dropped any, consider "trying" an iron supplement then.
Just some ideas. I strongly suggest that you get a complete workup done so they can try and get you balanced again. You can't afford to be passing out or losing your footing, especially in the shower. If you dont already have one, you might want to get a shower seat. Most pharmacies or drugstores carry them. It might help you through this time and get your full shower in a safer way. Make sure you take your showers when someone is home with you for awhile, or at least until this light headedness is cleared up.
Take care and let us know what the doc says and be careful. Tammy