I was doing deads for a while, but then I had a point a few years back where I'd do them and then hit abs after and get a cramp...
...then nearly black-out from that cramp. Like, to the point where I was laying down in the gym office because I couldn't make it out to the car. Ended updo going to the doc's and he said it was possible that I had a hernia, but I wouldn't know for sure unless I got a scan (which I didn't do). Since then, I've eased up to play it safe, but I've been tempted to go back to hitting deads (even if they're light) to test it out.
I don't know though.