In the root directory of the C: drive there is a hiberfil.sys file which is 6.2Gb. There is 8Gb of memory. Could the difference be memory allocated to file buffers and memory shared with GPU?
The online help for Windows could explain what I experienced:
'Hybrid sleep is designed primarily for desktop computers. Hybrid sleep is a combination of sleep and hibernate - €”it puts any open documents and programs in memory and on your hard disk, and then puts your computer into a low-power state so that you can quickly resume your work. That way, if a power failure occurs, Windows can restore your work from your hard disk. When hybrid sleep is turned on, putting your computer into sleep automatically puts your computer into hybrid sleep. Hybrid sleep is typically turned on by default on desktop computers.'