How do undo Excel list hiding entries

I keep a client list and excel at random will essentially hide entire rows of entries. For example if I go to search a name from the name column that I know I entered nothing will return but if I specifically enter the cell number that is hidden the information will be show, does excel 2011 have an auto-grouping or hiding feature that I'm not aware of? If so, how do I get rid of it?


I'm not sure if this makes a difference but all the numbers to the left most of the sheet are blue where in every other sheet they are gray.