In the first situation you describe, it can simply be a series of large orders being placed (large companies, hedge funds, etc.), which can also trigger additional orders by speculators.

In the second situation you describe, this is a practice known as stop hunting, where banks and brokers will intentionally and temporarily drive a currency pair in the opposite direction in order to wipe out traders' stops. Here's one of many articles you can find on the subject. The best way to counter this practice is to avoid tight stops, give them some room!