There are multiple factors that can cause the bull run to get reversed. Some of them are,

1. Negative legislation by major countries
2. Large amount of liquidation from. Corporate or government entities
3. Negative regulatory actions against big exchanges

I think these are main reason which can cause the current trend to get reversed. I know large liquidation is happening. Received Bhutan government has sold a decent amount of Bitcoin from their holdings. But that was expected.