I had that thought too.
When he called this morning and described, I suggested kidney or spleen. Kidney could be several things, but I worried about spleen because a rupture would be very dangerous.
When I sent out a message to friends the nurse immediately texted back I should call 911 for a heart attack!
I had a relative diagnosed with kidney stones that had cramps in the lower back area and the nausea, it’s why it came to mind. Fortunately something that can be treated. A cousin of mine had hers “zapped” to make them easier to pass.