Cells are so small they can't be read.

I have a workbook with a work sheet for each month. I was preparing the sheet for August and clicked and dragged the vertical scroll bar. The scroll bar began moving without me moving my pointer and finally made all cells so small that I can’t read them. I cannot find a way to reverse the action. It appears that all the data is still there but small. I tried using the format painter but that didn’t work. Currently, I have columns A thru CJ and rows 1 thru 172 showing on the screen. Anyone know what I might have hit and how to reverse it?