It's not just Steem but the whole cryptocurrency industry that goes up and down very fast. 100 billion down in market cap in a week is pretty standard these days. Eventually in the future it would be cool if it was a bit more stable but that will probably take a very long time. Since this market is expected to grow a lot in amount of users the next couple of years and even decades!
On the other hand it's way more fun than fiat currency that rarely goes up high in value! Clearly crypto is the future of transfer digital value on the Internet! If it goes down fast then it also can go up fast! Especially when we see Smart Media Tokens hit the market and companies have to keep a reserve of Steem!
Is there anyway for someone to know when a particular cryptocurrency is about to rise or fall
Nope. Since most humans are walking around unconscious for most of their day we really have no idea when they get crazy ideas and decides to sell or buy. The only thing we know is that when people start talking about Bitcoin going to the moon in the mainstream media then the price usually goes up!