Slipage indeed may occur in the forex market, this means that the execution of the desired price level misses or does not match your expectations when placing an order. In general, this is due to an imbalance of sellers and buyers.
In simple terms, an order can be fulfilled if some sellers and buyers order at the same price and lot size. When we place an order but there are no other orders that are exactly matched to fulfill it, then the price will be executed at the next best price. Trading during high-impact news releases is vulnerable to this condition, besides that broker technology is also another reason in this case. ECN brokers are usually the best choice because they can provide a high level of trading technology sophistication.