Try pressing the esc key. If that doesn't work, hover the cursor near the top of screen to see if toolbar/menu bar appears. If it does go to View, toolbars, click menu bar and any others you want. If that fails, maybe someone else can help.
Managed to get toolbars back - hovered cursor at top of screen and when toolbar descended I quickly clicked on Tools and then the drop-down menu indicated I must have selected "Full Screen" (though how I did that in the first place I have no idea!). So, de-selecting this option restored everything!
Thanks for your help! Brownie points on their way to you!