Actually I think the inversion tables are pretty safe. If you feel strong pressure in your head, eyes, whatever, just level out enoughthat it stops.
When I used to do Yoga headstands, it wasn't as easy to adjust out of it. Over the years I do seem to remember a couple of red eyes coming from popped blood vessels in the eye. But of my hundreds of headstands usually for 20 minutes at a time, I think it happened maybe twice. On the inversion table you can relieve any pressure instantly - so it shouldn't be an issue at all. Just don't be Evil Kneivel and push the envelope. If you feel more than mild pressure anywhere, just level back out and proceed slowly.