The choices that other advertisers, who are participating in the same auctions as you, make can affect your campaign’s performance. New advertisers or advertisers who adjust their existing accounts can affect how many impressions your ads receive.
Example
If an advertiser who is using the same targeting as you increases their bids, this may affect your ad's position on the first page of search results, leading to a drop in impressions. You may need to raise your bids or bid targets to recover lost impressions.
Need something else?
Check other common reasons why your campaign performance is fluctuating.