I have found a temporary solution : if I collapse all the panels : right click ob Folders -> collapse all then I get the Collections panel. If I then do: folders -> expand all the I cannot see the Collections panel anymore !!!
Thank you Ian for responding. No the solo mode is not ticked. I found out that I see the collections when I am in develop mode , not in Library mode un less I do what I said earlier : right click Folders -> collapse all
You shouldn't need to go and find Collapse All each time. Click in the heading for any panel that's taking up too much screen space, to collapse that, then again to open that up. Ctrl+click (Cmd+click) on any one panel, to do this to them all.
You should still always see the Collections panel when you scroll down beyond Folders, though. Unless it has been concealed (un-checked from appearing at all).