Thanks for the explanation, but it did not happened in previous weeks so I looked in my Options menu and yes, Health Check was selected - but not by me!
Has there been an update during the past week where Health Check has been set as the default home screen, or could an update have changed the setting in some way? If so I must disable automatic updates.
Whatever the cause it seems I have lost all my history. Having done a System Restore in an attempt to recover history (no success) it did recover all my bookmarks - thank goodness, so not all my work has not been lost.
I have just run Health Check and found there are ways to stop it deleting history etc. but unless a user is made aware of this it will do exactly what it has done to me. There should be a WARNING about using the Health Check option, and it should be made clear that selecting Health Check for 'CCleaner Home Screen' as shown in your reply above, means HC will be used whenever CCleaner is scheduled to run.