I think there are “circuit breakers”, which disable automated program trading - but there’s not an actual limit down. You just need to actually place the trades, after a large enough point swing.
As they say “don’t try to catch a falling knife”, but there are certainly all sorts of buy opportunities in someone’s future...
One system, which is private and subscription-only, is predicting a one hour shutdown of the markets tomorrow. Have no idea if that will happen, nor is it a good thing for anyone but insiders when it does happen.