This is not about traffic drop or page rank drop. Its about keyword ranking drop in serp's. A small site which is getting 5,500 impressions on 22-03-2013 drops to only 600 impressions on 23-03-2013. It slightly up on 07-04-2013 with 2,500 impressions but it was back to 600-700 impressions in next few days. Now its near 200-250 only. These are for all queries. Also for a specific query which is not affected on 23-03-2013, the impressions goes null on 07-04-2013 and after that. Was their any algorithm update on these dates.
[edited by: tedster at 5:39 pm (utc) on May 20, 2013] [edit reason] moved from another location [/edit]