People are getting info about November fork, we might see drop below 3600 in next 48 hours and before Nomber possibly to 3k or less, but 3k will probably be a huge support. Also 1/3 (33 %) of miners changed from btc mining to bitcoin cash mining. People will FUD, sell now, buy back later when bitcoin dips. Segwit 23 August was already priced in and we risk fiasco of unsuccessful segwit transactions and/or lost coins because of segwit security vulnerabilities. Even Slush pool CEO (inventor of bitcoin mining pools) said that he first needs to see segwit transactions, until then no one knows.
I don't think that if the price goes down it's about people getting to know about the potential november fork or anything like that. It's just that we haven't seen a sustained growth for a while now, price has just been floating around 4k-4.2k and going nowhere, and there are still margin traders out there that are paying interest on their loans. They probably think that btc isn't going to go much higher than this, so they close their long positions. This forces a lot more people to close their long positions essentially causing a chain reaction.
The most likely thing to happen is a dip at around $3500 lowest, and then rebound up to close to $4k before again correcting down to $3300 or so. Just my personal thoughts.