There are many factors that affect the rise and fall of Bitcoin both technical and fundamental point of view.

Fundamental Factors: If there is any news release from a particular country or governing body just like recent china's ban on ico and bitcoin exchanges then it may affect the bitcoin price for short term or long term. The affect depends on the news and where does its comes from, who is releasing the news etc and so on.

Technical Factors: There are also some kind of technical reasons or factors that may affect the rise and fall of BTC like Loss booking, Profit booking, Overbought, Oversold and chart patterns like Head & shoulders,Double top etc .