Since difficulty is increasing, there will be less mined bitcoins and thus less bitcoins sold by miners to pay for electricity and other costs, thus the BTC/USD should not fall, but rise right? (Less sell pressure).
If difficulty is increasing, it is because ASICs are being delivered, hashing power is constantly increasing, and blocks are found before 10 min on average. It will keep this way, meaning that more buying will be mined, quicker, and price will decrease