There are only very few exchanges are providing such facility of trading "short" with bitcoin markets. If you are serious to find one then I guess you must check with few forex brokers who are also providing bitcoin trading. I read bitfinex is providing such type of trading but I checked and could not find any new thing to do so.

Bitcoin is in bearish mode, bitcoin is in bullish mode, bitcoin is very moody, I can almost say it is bipolar. One day it goes up and we are all happy and we want to see 50k and we want to get rich and be happy and have lambo and get a penthouse, the next day we see bitcoin going down, we start to talk about how it will go to 2k , how we will all be poor, how we will be going to get food from shelters and lose all we have trying to drop the averages. I think the volatility in bitcoins mood is actually affecting our mood as well, heavily, most of us here have their days happy or sad according to how bitcoin is going. Lately we have all been quite sad.