When streaming videos in safari, my cursor often disappears.

Troubleshoot Safari extensions ..

From the Safari menu bar click Safari > Preferences then select the Extensions tab. Turn that OFF, quit and relaunch Safari to test.

If that helped, turn one extension on then quit and relaunch Safari to test until you find the incompatible extension then click uninstall.

If it's not an extensions issue ...

From your Safari menu bar click Safari > Preferences then select the Privacy tab.

Click: Remove All Website Data

Open System Preferences > Flash Player then select the Advanced tab.

Click Delete All under Browsing Data and Settings

Not empty the Safari cache.

From your Safari menu bar click Safari > Preferences then select the Advanced tab.

Select: Show Develop menu in menu bar

Now click Develop from the menu bar. From the drop down menu click Empty Caches. Now try a video.

And make sure your OS X software is up to date.

Click the Apple  top left in your screen.

From the drop down menu click: Software Update

I am watching the cricket on streaming video on SkyGo right now.

I can create this problem, although it has never bothered me, by clicking on the video section which brings up a pop up from Sky telling me which channel I am watching. When that automatically closes after a few seconds it also turns off the cursor.

Get it back by running the mouse up and down to the top and bottom of the screen (even though you cannot see it) then it reappears.

Somebody clever might be able to explain why?