Open Office Calc problem

Am I the only one who has had this happen? Google comes up blank...

I have a large spreadsheet—sales for the last 24 months, 34000+ lines—that I did a subtotal calculation on. I collapsed the data so that all I see is the subtotals, then I saved it. Now, I reopen the sheet and the subtotals are all there, complete with the formulas in the cells, but I can't expand it to see the detail anymore! I've tried selecting it all and redoing the subtotals, in case the data would reappear. Nope!

Anybody know what I can do? Sure, I can recreate it or restore a backup (I use Time Machine—a wonderful tool!), but I've done lots of stuff on the file since then that I would like to keep...Frustration!!!!!