Weird laptop failing

You know that bar on the RH side of the screen with a little arrow at the top and bottom to make things scroll up and down ? (If it has a technical term please feel free to enlighten me.) Also the little blue section in the middle of the bar for the same?

Well, today, my bottom arrow is not working. Blue strip works OK, top arrow works OK.

Luckily, the downward triangle key is doing the job, otherwise the laptop would be through the window with frustration by now. But it's a bit weird. What has happened to it and can I fix it?

 

The technical term for it is 'the scroll bar'.

 

Please explain what you mean by "bottom arrow" and "downward triangle key" Do you mean the up/down controls on the scroll bar, or do you mean up/down arrows on your keyboard (how are they working?).

 

I meant the top and bottom arrows on the scroll bar itself, but also referred to the down arrow on the keyboard.
However, having switched off whilst out shopping, and switched back on I find it has now cured itself. So Loofah must be right. The Gremlins got bored.

 

I only got totally confused after reading it once.

 

That always should be the first attempt at rectification

 

I should have thought of it before.