Here are some charts (using horrible Coinbase charts, because they are easy to read) that illustrate some of the points, but before you look at them, please note the entire post (like towards the end of the charts, the dips in all the currencies shown, and the sometimes there is a bit of lag before the values reflect in the other currency, as well as the correlations now being off as most cryptos have started to fall in synchronicity with one another):
For even further clarification, obviously read the post, and if you want to see something more real time, which is harder for me to capture and illustrate, load up an exchange like Gemini or GDAX or whatever, and watch the candles for BTC. When they start to make big moves in one direction or another, it usually only takes a minute or two before LTC, ETH, etc. follow along. It is actually a fairly solid indicator of if a currency is going to go up or down slightly in advance, although there are times when the prices do stray in various directions, depending on the ledgers and the current buy/sell orders (is there is a sell wall at a certain amount on LTC, you're not going to be following as closely to BTC as you might expect, so keep an eye out for any whales or massive buy/sell on the particular crypto you are watching)
Pretty much all cryptos were soaring before Coinbase adopted BCH. The dips in other currencies, such as LTC, ETH and BTC, especially, seem to be inversely tied to whatever rises and falls BCH experiences.
Various currencies are not intrinsically linked by the minute, in particular, LTC and others seem to lag a bit behind whatever BTC is doing, sometimes having wild fluctuations before aligning more properly with BTC over a slightly longer time block.
Before going too much further into this, keep in mind that a lot of cryptos are generally following the swings of BTC... huge gains for BTC usually are mirrored, as well as falling values.
Now, if you look at BCH, you can see something rather different. BCH, almost always, rises as BTC falls, and vice-versa. One might think this represents some kind of confidence in such a currency, or distrust when it falls, and that seems like a valid explanation, but an easier way of thinking about it is like this: BCH is literally "sucking value" out of the other cryptos, hitting BTC and then cascading down through the others.
How much has BTC fallen since BCH hit Coinbase? Nearly the value of BCH, and then somewhat stabilized. There is a direct correlation between the value of BCH at any given time and the value of BTC, but there is also a type of lag, as is seen when other cryptos follow BTC, except for this lag can be more pronounced - as the correlation is one where, typically, the linked values are realized on the market at a slower pace.
We're likely going to see a sort of stabilization soon. If you're waiting for the price of BTC to go back up, be on the lookout for BCH to start falling. Sometimes the two cryptos will decline together, this is because people are losing faith in the market and converting back to fiat, or "cashing out". This could trigger a type of spiral where all cryptos lose a lot of value rather quickly: especially as some parts of the world are experiencing holidays where having fiat on hand would make sense to the average person.
This isn't all bad news, BTC and other cryptos were due for an adjustment. You actually should look at the positive thing that is happening now, and that is that, whatever crypto you prefer, you will (soon) be able to buy back in at a much more manageable price point.
Think about it this way, if BTC is worth $20,000 and you want to double your money, then you must wait for BTC to become worth $40,000 - which a couple of weeks ago did not seem like a bad prospect.
Most of these cryptos WILL recover, it is inevitable. The technology has not changed, the concept has not changed, just a rogue competitor temporarily soaked up some of the value from other major cryptos. It might sustain some of that value, but once the market properly adjusts, the cryptos should go back up.
As I am typing this, BTC and other cryptos are literally in an almost free fall state. I try to look on the positive side. If you own ten ETH or ten LTC instead of 0.1 of either, then you will be better off day trading and trying to profit off of volatility. If you've been HODL, you can keep HODL and rest assured the prices will recover. Weak hands right now are further driving the market down.