I think the dangerous price is when the market value is decreases lower than fifty percent.
Because from this it is very alarming most especially when it happens very quickly. We should be alarm from this and be alert in order not to suffer in huge loss which is a big nightmare for all of us.
That would be a dangerous indicator and not a dangerous price. A 50% loss in price would mean a huge amount of market capitalization being dumped and cashed out. It would only mean that some big whale or a bunch of whales have sieved off their money from the market and moving it elsewhere. You might also see this if some news is made - but that news would be having a huge impact and thats tough to think of.
In any of these cases its not possible that the price will remain low. It will be a good point of entry for some people and they will buy in. When someone sells another person buy. Thats how the market works.