If you comes across a situation where an Excel spreadsheet is open but not visible, you may find that it has been hidden by a user in a way that they did not understand.
The normal way to hide a sheet it to right click on it and click the hide option or go via the HOME tab as shown below
If you do it this way, the spreadsheet workbook remains visible but the sheet is hidden. To get it back you click on any of the other sheets and then click UNHIDE.
However, sometimes when you open a workbook, you see that it is open but you can’t actually see it. This could be as a result of an intentional or accidental hiding of the workbook (as apposed to a sheet).
Under the VIEW tab you will see buttons called Hide and Unhide.
It is easy to assume that this relates to the sheet you are on, but in fact it relates to the whole workbook. If you click HIDE, the workbook will disappear but it is still operational and open.
In order to see it again, click the UNHIDE option in the VIEW tab and it will give you a list of hidden workbooks. You can then choose the one you want to see and click OK, and it will re appear,