Help! My menu bars(?) in Chrome keep disappearing

That is probably the wrong name for them, sorry. At the top of my Chrome window there are normally three lines of info/tools above the actual webpage site. From the top:
First, a line with a down arrow that accesses open and recently closed tabs, then the name/icons of the various tabs I’ve opened.
Second, a line with ‘go back’ ‘go forward’ ‘reload’ ‘home’ and then the name of the tab currently open, then a bunch of icons including ‘make a bookmark’ and ‘open ad blocker’ and finally the three dot thing that opens a menu of stuff.
Third, the actual bookmark bar.

The past few days all of that has vanished from the screen at times, but not because of anything I’ve deliberately done. Just now it happened when I was completely out of the room for fifteen minutes. When I left, things were normal. When I came back, all three top bars had vanished, and the Straight Dope web page basically filled the whole screen. This leaves me with no icons to maneuver from page to page. In fact, the only way I’ve found to end this is to use control-alt-delete, chose the Task Manager, and then select and close Chrome. I can reopen Chrome, and it looks normal then, but I’ve lost the tabs I’ve chosen to open (basically, the list of the threads I wanted to read, but hadn’t gotten to yet.) This makes me sad.

Two questions:

Am I doing something that causes this to happen, some accidental key touch?

When it happens, how do I get my normal menu bars back again? Without having to lose my chosen tabs, hopefully.

Thanks for the helpful wisdom I hope to receive!

This sounds like it went fullscreen. Try the F11 key to toggle between fullscreen and normal mode.

Oh, wonderful! That worked perfectly.

And I think I know what happened. I have a messy desk, and just before I left the room this time, I’d laid several pieces of paper on top of the keyboard as I was sorting things out, before taking them off to other rooms to deal with. I must have accidentally pushed F11 while setting down or picking up something. So my screen actually changed before I left, but my attention was elsewhere and I didn’t see it until my return.

So mystery solved, thank you again!

(I must confess, I have no idea what any of the function keys are for. I’ve never used them for anything.)

Great!

Us nerds use the F keys quite a bit, but their presence is pretty much a waste of space to most users.

My Mac has a “virtual” extra line above the keyboard, it is a long thin touch screen that has the F keys and a bunch more on it (depending on what you are doing) and I love it.

My favourite in-office entertainment is to casually reply “Alt-F4” to people who have any problem and ask out loud - any problem at all - but this closes the current window. Doesn’t exactly solve the problem.