i was surprised to see the market today, everything fell in a short time, bitcoin fell around $1000 very fast and looking at coinmarketcap, all coins are red. a few days ago bitcoin rose slowly, but today was very surprising. What happen today?

It's just another day of "correction" as you cannot predict when will it be exactly happening.
Looks like the BTC bulls cannot keep up to sustain a certain range which results for the market to go down a bit.
As of today, we are still in the bear market so these mini bull runs are just short term only. We just don't know when will the market go up again. It's unpredictable.