It all depends on the strategy you are using. Sometimes a strategy could have such series under the specific market conditions. For example, trend-based strategies could generate series like this during the flat movement. In other words, first of all you need to understand the reason: whether it caused by underperformance of the strategy itself or due to the mistakes made by the trader. By the way, the easiest way to check the performance of the strategy in long term perspective is to test it using special software like Forex Tester, that executes simulated trades using historical data provided by brokers. Such testing could show you that, for example, 5 losses in a row is absolutely normal for your strategy, or such situations could take place under some specific market conditions. At the same time, testing could also show that such situations aren`t common for your strategy. In this case, you will have to search for the mistake in your actions and trading decisions.
Anyway, as it was mentioned before, you should try to reduce psychological impact of such loss. It is great that you pay attention to issues like this, so hope you will be able to deal with it.